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1
390-393
It follows straight from the fact that Coulomb’s law is consistent with Newton’s third law The proof is left to you as an exercise 1 7 ELECTRIC FIELD Let us consider a point charge Q placed in vacuum, at the origin O
1
391-394
The proof is left to you as an exercise 1 7 ELECTRIC FIELD Let us consider a point charge Q placed in vacuum, at the origin O If we place another point charge q at a point P, where OP = r, then the charge Q will exert a force on q as per Coulomb’s law
1
392-395
1 7 ELECTRIC FIELD Let us consider a point charge Q placed in vacuum, at the origin O If we place another point charge q at a point P, where OP = r, then the charge Q will exert a force on q as per Coulomb’s law We may ask the question: If charge q is removed, then what is left in the surrounding
1
393-396
7 ELECTRIC FIELD Let us consider a point charge Q placed in vacuum, at the origin O If we place another point charge q at a point P, where OP = r, then the charge Q will exert a force on q as per Coulomb’s law We may ask the question: If charge q is removed, then what is left in the surrounding Is there nothing
1
394-397
If we place another point charge q at a point P, where OP = r, then the charge Q will exert a force on q as per Coulomb’s law We may ask the question: If charge q is removed, then what is left in the surrounding Is there nothing If there is nothing at the point P, then how does a force act when we place the charge q at P
1
395-398
We may ask the question: If charge q is removed, then what is left in the surrounding Is there nothing If there is nothing at the point P, then how does a force act when we place the charge q at P In order to answer such questions, the early scientists introduced the concept of field
1
396-399
Is there nothing If there is nothing at the point P, then how does a force act when we place the charge q at P In order to answer such questions, the early scientists introduced the concept of field According to this, we say that the charge Q produces an electric field everywhere in the surrounding
1
397-400
If there is nothing at the point P, then how does a force act when we place the charge q at P In order to answer such questions, the early scientists introduced the concept of field According to this, we say that the charge Q produces an electric field everywhere in the surrounding When another charge q is brought at some point P, the field there acts on it and produces a force
1
398-401
In order to answer such questions, the early scientists introduced the concept of field According to this, we say that the charge Q produces an electric field everywhere in the surrounding When another charge q is brought at some point P, the field there acts on it and produces a force The electric field produced by the charge Q at a point r is given as E r r r ( ) = = 41 41 0 2 0 2 π π ε ε rQ rQ ˆ ˆ (1
1
399-402
According to this, we say that the charge Q produces an electric field everywhere in the surrounding When another charge q is brought at some point P, the field there acts on it and produces a force The electric field produced by the charge Q at a point r is given as E r r r ( ) = = 41 41 0 2 0 2 π π ε ε rQ rQ ˆ ˆ (1 6) where ˆ = r r/r, is a unit vector from the origin to the point r
1
400-403
When another charge q is brought at some point P, the field there acts on it and produces a force The electric field produced by the charge Q at a point r is given as E r r r ( ) = = 41 41 0 2 0 2 π π ε ε rQ rQ ˆ ˆ (1 6) where ˆ = r r/r, is a unit vector from the origin to the point r Thus, Eq
1
401-404
The electric field produced by the charge Q at a point r is given as E r r r ( ) = = 41 41 0 2 0 2 π π ε ε rQ rQ ˆ ˆ (1 6) where ˆ = r r/r, is a unit vector from the origin to the point r Thus, Eq (1
1
402-405
6) where ˆ = r r/r, is a unit vector from the origin to the point r Thus, Eq (1 6) specifies the value of the electric field for each value of the position vector r
1
403-406
Thus, Eq (1 6) specifies the value of the electric field for each value of the position vector r The word “field” signifies how some distributed quantity (which could be a scalar or a vector) varies with position
1
404-407
(1 6) specifies the value of the electric field for each value of the position vector r The word “field” signifies how some distributed quantity (which could be a scalar or a vector) varies with position The effect of the charge has been incorporated in the existence of the electric field
1
405-408
6) specifies the value of the electric field for each value of the position vector r The word “field” signifies how some distributed quantity (which could be a scalar or a vector) varies with position The effect of the charge has been incorporated in the existence of the electric field We obtain the force F exerted by a charge Q on a charge q, as F r = 41 0 2 πε rQq ˆ (1
1
406-409
The word “field” signifies how some distributed quantity (which could be a scalar or a vector) varies with position The effect of the charge has been incorporated in the existence of the electric field We obtain the force F exerted by a charge Q on a charge q, as F r = 41 0 2 πε rQq ˆ (1 7) Note that the charge q also exerts an equal and opposite force on the charge Q
1
407-410
The effect of the charge has been incorporated in the existence of the electric field We obtain the force F exerted by a charge Q on a charge q, as F r = 41 0 2 πε rQq ˆ (1 7) Note that the charge q also exerts an equal and opposite force on the charge Q The electrostatic force between the charges Q and q can be looked upon as an interaction between charge q and the electric field of Q and vice versa
1
408-411
We obtain the force F exerted by a charge Q on a charge q, as F r = 41 0 2 πε rQq ˆ (1 7) Note that the charge q also exerts an equal and opposite force on the charge Q The electrostatic force between the charges Q and q can be looked upon as an interaction between charge q and the electric field of Q and vice versa If we denote the position of charge q by the vector r, it experiences a force F equal to the charge q multiplied by the electric field E at the location of q
1
409-412
7) Note that the charge q also exerts an equal and opposite force on the charge Q The electrostatic force between the charges Q and q can be looked upon as an interaction between charge q and the electric field of Q and vice versa If we denote the position of charge q by the vector r, it experiences a force F equal to the charge q multiplied by the electric field E at the location of q Thus, F(r) = q E(r) (1
1
410-413
The electrostatic force between the charges Q and q can be looked upon as an interaction between charge q and the electric field of Q and vice versa If we denote the position of charge q by the vector r, it experiences a force F equal to the charge q multiplied by the electric field E at the location of q Thus, F(r) = q E(r) (1 8) Equation (1
1
411-414
If we denote the position of charge q by the vector r, it experiences a force F equal to the charge q multiplied by the electric field E at the location of q Thus, F(r) = q E(r) (1 8) Equation (1 8) defines the SI unit of electric field as N/C*
1
412-415
Thus, F(r) = q E(r) (1 8) Equation (1 8) defines the SI unit of electric field as N/C* Some important remarks may be made here: (i) From Eq
1
413-416
8) Equation (1 8) defines the SI unit of electric field as N/C* Some important remarks may be made here: (i) From Eq (1
1
414-417
8) defines the SI unit of electric field as N/C* Some important remarks may be made here: (i) From Eq (1 8), we can infer that if q is unity, the electric field due to a charge Q is numerically equal to the force exerted by it
1
415-418
Some important remarks may be made here: (i) From Eq (1 8), we can infer that if q is unity, the electric field due to a charge Q is numerically equal to the force exerted by it Thus, the electric field due to a charge Q at a point in space may be defined as the force that a unit positive charge would experience if placed * An alternate unit V/m will be introduced in the next chapter
1
416-419
(1 8), we can infer that if q is unity, the electric field due to a charge Q is numerically equal to the force exerted by it Thus, the electric field due to a charge Q at a point in space may be defined as the force that a unit positive charge would experience if placed * An alternate unit V/m will be introduced in the next chapter FIGURE 1
1
417-420
8), we can infer that if q is unity, the electric field due to a charge Q is numerically equal to the force exerted by it Thus, the electric field due to a charge Q at a point in space may be defined as the force that a unit positive charge would experience if placed * An alternate unit V/m will be introduced in the next chapter FIGURE 1 8 Electric field (a) due to a charge Q, (b) due to a charge –Q
1
418-421
Thus, the electric field due to a charge Q at a point in space may be defined as the force that a unit positive charge would experience if placed * An alternate unit V/m will be introduced in the next chapter FIGURE 1 8 Electric field (a) due to a charge Q, (b) due to a charge –Q Rationalised 2023-24 Electric Charges and Fields 15 at that point
1
419-422
FIGURE 1 8 Electric field (a) due to a charge Q, (b) due to a charge –Q Rationalised 2023-24 Electric Charges and Fields 15 at that point The charge Q, which is producing the electric field, is called a source charge and the charge q, which tests the effect of a source charge, is called a test charge
1
420-423
8 Electric field (a) due to a charge Q, (b) due to a charge –Q Rationalised 2023-24 Electric Charges and Fields 15 at that point The charge Q, which is producing the electric field, is called a source charge and the charge q, which tests the effect of a source charge, is called a test charge Note that the source charge Q must remain at its original location
1
421-424
Rationalised 2023-24 Electric Charges and Fields 15 at that point The charge Q, which is producing the electric field, is called a source charge and the charge q, which tests the effect of a source charge, is called a test charge Note that the source charge Q must remain at its original location However, if a charge q is brought at any point around Q, Q itself is bound to experience an electrical force due to q and will tend to move
1
422-425
The charge Q, which is producing the electric field, is called a source charge and the charge q, which tests the effect of a source charge, is called a test charge Note that the source charge Q must remain at its original location However, if a charge q is brought at any point around Q, Q itself is bound to experience an electrical force due to q and will tend to move A way out of this difficulty is to make q negligibly small
1
423-426
Note that the source charge Q must remain at its original location However, if a charge q is brought at any point around Q, Q itself is bound to experience an electrical force due to q and will tend to move A way out of this difficulty is to make q negligibly small The force F is then negligibly small but the ratio F/q is finite and defines the electric field: E F =   → qlim q 0 (1
1
424-427
However, if a charge q is brought at any point around Q, Q itself is bound to experience an electrical force due to q and will tend to move A way out of this difficulty is to make q negligibly small The force F is then negligibly small but the ratio F/q is finite and defines the electric field: E F =   → qlim q 0 (1 9) A practical way to get around the problem (of keeping Q undisturbed in the presence of q) is to hold Q to its location by unspecified forces
1
425-428
A way out of this difficulty is to make q negligibly small The force F is then negligibly small but the ratio F/q is finite and defines the electric field: E F =   → qlim q 0 (1 9) A practical way to get around the problem (of keeping Q undisturbed in the presence of q) is to hold Q to its location by unspecified forces This may look strange but actually this is what happens in practice
1
426-429
The force F is then negligibly small but the ratio F/q is finite and defines the electric field: E F =   → qlim q 0 (1 9) A practical way to get around the problem (of keeping Q undisturbed in the presence of q) is to hold Q to its location by unspecified forces This may look strange but actually this is what happens in practice When we are considering the electric force on a test charge q due to a charged planar sheet (Section 1
1
427-430
9) A practical way to get around the problem (of keeping Q undisturbed in the presence of q) is to hold Q to its location by unspecified forces This may look strange but actually this is what happens in practice When we are considering the electric force on a test charge q due to a charged planar sheet (Section 1 14), the charges on the sheet are held to their locations by the forces due to the unspecified charged constituents inside the sheet
1
428-431
This may look strange but actually this is what happens in practice When we are considering the electric force on a test charge q due to a charged planar sheet (Section 1 14), the charges on the sheet are held to their locations by the forces due to the unspecified charged constituents inside the sheet (ii) Note that the electric field E due to Q, though defined operationally in terms of some test charge q, is independent of q
1
429-432
When we are considering the electric force on a test charge q due to a charged planar sheet (Section 1 14), the charges on the sheet are held to their locations by the forces due to the unspecified charged constituents inside the sheet (ii) Note that the electric field E due to Q, though defined operationally in terms of some test charge q, is independent of q This is because F is proportional to q, so the ratio F/q does not depend on q
1
430-433
14), the charges on the sheet are held to their locations by the forces due to the unspecified charged constituents inside the sheet (ii) Note that the electric field E due to Q, though defined operationally in terms of some test charge q, is independent of q This is because F is proportional to q, so the ratio F/q does not depend on q The force F on the charge q due to the charge Q depends on the particular location of charge q which may take any value in the space around the charge Q
1
431-434
(ii) Note that the electric field E due to Q, though defined operationally in terms of some test charge q, is independent of q This is because F is proportional to q, so the ratio F/q does not depend on q The force F on the charge q due to the charge Q depends on the particular location of charge q which may take any value in the space around the charge Q Thus, the electric field E due to Q is also dependent on the space coordinate r
1
432-435
This is because F is proportional to q, so the ratio F/q does not depend on q The force F on the charge q due to the charge Q depends on the particular location of charge q which may take any value in the space around the charge Q Thus, the electric field E due to Q is also dependent on the space coordinate r For different positions of the charge q all over the space, we get different values of electric field E
1
433-436
The force F on the charge q due to the charge Q depends on the particular location of charge q which may take any value in the space around the charge Q Thus, the electric field E due to Q is also dependent on the space coordinate r For different positions of the charge q all over the space, we get different values of electric field E The field exists at every point in three-dimensional space
1
434-437
Thus, the electric field E due to Q is also dependent on the space coordinate r For different positions of the charge q all over the space, we get different values of electric field E The field exists at every point in three-dimensional space (iii) For a positive charge, the electric field will be directed radially outwards from the charge
1
435-438
For different positions of the charge q all over the space, we get different values of electric field E The field exists at every point in three-dimensional space (iii) For a positive charge, the electric field will be directed radially outwards from the charge On the other hand, if the source charge is negative, the electric field vector, at each point, points radially inwards
1
436-439
The field exists at every point in three-dimensional space (iii) For a positive charge, the electric field will be directed radially outwards from the charge On the other hand, if the source charge is negative, the electric field vector, at each point, points radially inwards (iv) Since the magnitude of the force F on charge q due to charge Q depends only on the distance r of the charge q from charge Q, the magnitude of the electric field E will also depend only on the distance r
1
437-440
(iii) For a positive charge, the electric field will be directed radially outwards from the charge On the other hand, if the source charge is negative, the electric field vector, at each point, points radially inwards (iv) Since the magnitude of the force F on charge q due to charge Q depends only on the distance r of the charge q from charge Q, the magnitude of the electric field E will also depend only on the distance r Thus at equal distances from the charge Q, the magnitude of its electric field E is same
1
438-441
On the other hand, if the source charge is negative, the electric field vector, at each point, points radially inwards (iv) Since the magnitude of the force F on charge q due to charge Q depends only on the distance r of the charge q from charge Q, the magnitude of the electric field E will also depend only on the distance r Thus at equal distances from the charge Q, the magnitude of its electric field E is same The magnitude of electric field E due to a point charge is thus same on a sphere with the point charge at its centre; in other words, it has a spherical symmetry
1
439-442
(iv) Since the magnitude of the force F on charge q due to charge Q depends only on the distance r of the charge q from charge Q, the magnitude of the electric field E will also depend only on the distance r Thus at equal distances from the charge Q, the magnitude of its electric field E is same The magnitude of electric field E due to a point charge is thus same on a sphere with the point charge at its centre; in other words, it has a spherical symmetry 1
1
440-443
Thus at equal distances from the charge Q, the magnitude of its electric field E is same The magnitude of electric field E due to a point charge is thus same on a sphere with the point charge at its centre; in other words, it has a spherical symmetry 1 7
1
441-444
The magnitude of electric field E due to a point charge is thus same on a sphere with the point charge at its centre; in other words, it has a spherical symmetry 1 7 1 Electric field due to a system of charges Consider a system of charges q1, q2,
1
442-445
1 7 1 Electric field due to a system of charges Consider a system of charges q1, q2, , qn with position vectors r1, r2,
1
443-446
7 1 Electric field due to a system of charges Consider a system of charges q1, q2, , qn with position vectors r1, r2, , rn relative to some origin O
1
444-447
1 Electric field due to a system of charges Consider a system of charges q1, q2, , qn with position vectors r1, r2, , rn relative to some origin O Like the electric field at a point in space due to a single charge, electric field at a point in space due to the system of charges is defined to be the force experienced by a unit test charge placed at that point, without disturbing the original positions of charges q1, q2,
1
445-448
, qn with position vectors r1, r2, , rn relative to some origin O Like the electric field at a point in space due to a single charge, electric field at a point in space due to the system of charges is defined to be the force experienced by a unit test charge placed at that point, without disturbing the original positions of charges q1, q2, , qn
1
446-449
, rn relative to some origin O Like the electric field at a point in space due to a single charge, electric field at a point in space due to the system of charges is defined to be the force experienced by a unit test charge placed at that point, without disturbing the original positions of charges q1, q2, , qn We can use Coulomb’s law and the superposition principle to determine this field at a point P denoted by position vector r
1
447-450
Like the electric field at a point in space due to a single charge, electric field at a point in space due to the system of charges is defined to be the force experienced by a unit test charge placed at that point, without disturbing the original positions of charges q1, q2, , qn We can use Coulomb’s law and the superposition principle to determine this field at a point P denoted by position vector r Rationalised 2023-24 16 Physics Electric field E1 at r due to q1 at r1 is given by E1 = 41 0 1 1 2 πε q r P 1P ˆr where 1P ˆr is a unit vector in the direction from q1 to P, and r1P is the distance between q1 and P
1
448-451
, qn We can use Coulomb’s law and the superposition principle to determine this field at a point P denoted by position vector r Rationalised 2023-24 16 Physics Electric field E1 at r due to q1 at r1 is given by E1 = 41 0 1 1 2 πε q r P 1P ˆr where 1P ˆr is a unit vector in the direction from q1 to P, and r1P is the distance between q1 and P In the same manner, electric field E2 at r due to q2 at r2 is E2 = 41 0 2 2 2 πε q r P 2P ˆr where ˆr2P is a unit vector in the direction from q2 to P and r2P is the distance between q2 and P
1
449-452
We can use Coulomb’s law and the superposition principle to determine this field at a point P denoted by position vector r Rationalised 2023-24 16 Physics Electric field E1 at r due to q1 at r1 is given by E1 = 41 0 1 1 2 πε q r P 1P ˆr where 1P ˆr is a unit vector in the direction from q1 to P, and r1P is the distance between q1 and P In the same manner, electric field E2 at r due to q2 at r2 is E2 = 41 0 2 2 2 πε q r P 2P ˆr where ˆr2P is a unit vector in the direction from q2 to P and r2P is the distance between q2 and P Similar expressions hold good for fields E3, E4,
1
450-453
Rationalised 2023-24 16 Physics Electric field E1 at r due to q1 at r1 is given by E1 = 41 0 1 1 2 πε q r P 1P ˆr where 1P ˆr is a unit vector in the direction from q1 to P, and r1P is the distance between q1 and P In the same manner, electric field E2 at r due to q2 at r2 is E2 = 41 0 2 2 2 πε q r P 2P ˆr where ˆr2P is a unit vector in the direction from q2 to P and r2P is the distance between q2 and P Similar expressions hold good for fields E3, E4, , En due to charges q3, q4,
1
451-454
In the same manner, electric field E2 at r due to q2 at r2 is E2 = 41 0 2 2 2 πε q r P 2P ˆr where ˆr2P is a unit vector in the direction from q2 to P and r2P is the distance between q2 and P Similar expressions hold good for fields E3, E4, , En due to charges q3, q4, , qn
1
452-455
Similar expressions hold good for fields E3, E4, , En due to charges q3, q4, , qn By the superposition principle, the electric field E at r due to the system of charges is (as shown in Fig
1
453-456
, En due to charges q3, q4, , qn By the superposition principle, the electric field E at r due to the system of charges is (as shown in Fig 1
1
454-457
, qn By the superposition principle, the electric field E at r due to the system of charges is (as shown in Fig 1 9) E(r) = E1 (r) + E2 (r) + … + En(r) = 41 41 41 0 1 1 2 1 0 2 2 2 2 0 2 π π π ε ε ε rq rq q r n n n P P P P P P ˆ ˆ
1
455-458
By the superposition principle, the electric field E at r due to the system of charges is (as shown in Fig 1 9) E(r) = E1 (r) + E2 (r) + … + En(r) = 41 41 41 0 1 1 2 1 0 2 2 2 2 0 2 π π π ε ε ε rq rq q r n n n P P P P P P ˆ ˆ ˆ r r r + + + E(r) = =∑ 41 0 P i P πε q r i i i n 2 1 ˆr (1
1
456-459
1 9) E(r) = E1 (r) + E2 (r) + … + En(r) = 41 41 41 0 1 1 2 1 0 2 2 2 2 0 2 π π π ε ε ε rq rq q r n n n P P P P P P ˆ ˆ ˆ r r r + + + E(r) = =∑ 41 0 P i P πε q r i i i n 2 1 ˆr (1 10) E is a vector quantity that varies from one point to another point in space and is determined from the positions of the source charges
1
457-460
9) E(r) = E1 (r) + E2 (r) + … + En(r) = 41 41 41 0 1 1 2 1 0 2 2 2 2 0 2 π π π ε ε ε rq rq q r n n n P P P P P P ˆ ˆ ˆ r r r + + + E(r) = =∑ 41 0 P i P πε q r i i i n 2 1 ˆr (1 10) E is a vector quantity that varies from one point to another point in space and is determined from the positions of the source charges 1
1
458-461
ˆ r r r + + + E(r) = =∑ 41 0 P i P πε q r i i i n 2 1 ˆr (1 10) E is a vector quantity that varies from one point to another point in space and is determined from the positions of the source charges 1 7
1
459-462
10) E is a vector quantity that varies from one point to another point in space and is determined from the positions of the source charges 1 7 2 Physical significance of electric field You may wonder why the notion of electric field has been introduced here at all
1
460-463
1 7 2 Physical significance of electric field You may wonder why the notion of electric field has been introduced here at all After all, for any system of charges, the measurable quantity is the force on a charge which can be directly determined using Coulomb’s law and the superposition principle [Eq
1
461-464
7 2 Physical significance of electric field You may wonder why the notion of electric field has been introduced here at all After all, for any system of charges, the measurable quantity is the force on a charge which can be directly determined using Coulomb’s law and the superposition principle [Eq (1
1
462-465
2 Physical significance of electric field You may wonder why the notion of electric field has been introduced here at all After all, for any system of charges, the measurable quantity is the force on a charge which can be directly determined using Coulomb’s law and the superposition principle [Eq (1 5)]
1
463-466
After all, for any system of charges, the measurable quantity is the force on a charge which can be directly determined using Coulomb’s law and the superposition principle [Eq (1 5)] Why then introduce this intermediate quantity called the electric field
1
464-467
(1 5)] Why then introduce this intermediate quantity called the electric field For electrostatics, the concept of electric field is convenient, but not really necessary
1
465-468
5)] Why then introduce this intermediate quantity called the electric field For electrostatics, the concept of electric field is convenient, but not really necessary Electric field is an elegant way of characterising the electrical environment of a system of charges
1
466-469
Why then introduce this intermediate quantity called the electric field For electrostatics, the concept of electric field is convenient, but not really necessary Electric field is an elegant way of characterising the electrical environment of a system of charges Electric field at a point in the space around a system of charges tells you the force a unit positive test charge would experience if placed at that point (without disturbing the system)
1
467-470
For electrostatics, the concept of electric field is convenient, but not really necessary Electric field is an elegant way of characterising the electrical environment of a system of charges Electric field at a point in the space around a system of charges tells you the force a unit positive test charge would experience if placed at that point (without disturbing the system) Electric field is a characteristic of the system of charges and is independent of the test charge that you place at a point to determine the field
1
468-471
Electric field is an elegant way of characterising the electrical environment of a system of charges Electric field at a point in the space around a system of charges tells you the force a unit positive test charge would experience if placed at that point (without disturbing the system) Electric field is a characteristic of the system of charges and is independent of the test charge that you place at a point to determine the field The term field in physics generally refers to a quantity that is defined at every point in space and may vary from point to point
1
469-472
Electric field at a point in the space around a system of charges tells you the force a unit positive test charge would experience if placed at that point (without disturbing the system) Electric field is a characteristic of the system of charges and is independent of the test charge that you place at a point to determine the field The term field in physics generally refers to a quantity that is defined at every point in space and may vary from point to point Electric field is a vector field, since force is a vector quantity
1
470-473
Electric field is a characteristic of the system of charges and is independent of the test charge that you place at a point to determine the field The term field in physics generally refers to a quantity that is defined at every point in space and may vary from point to point Electric field is a vector field, since force is a vector quantity The true physical significance of the concept of electric field, however, emerges only when we go beyond electrostatics and deal with time- dependent electromagnetic phenomena
1
471-474
The term field in physics generally refers to a quantity that is defined at every point in space and may vary from point to point Electric field is a vector field, since force is a vector quantity The true physical significance of the concept of electric field, however, emerges only when we go beyond electrostatics and deal with time- dependent electromagnetic phenomena Suppose we consider the force between two distant charges q1, q2 in accelerated motion
1
472-475
Electric field is a vector field, since force is a vector quantity The true physical significance of the concept of electric field, however, emerges only when we go beyond electrostatics and deal with time- dependent electromagnetic phenomena Suppose we consider the force between two distant charges q1, q2 in accelerated motion Now the greatest speed with which a signal or information can go from one point to another is c, the speed of light
1
473-476
The true physical significance of the concept of electric field, however, emerges only when we go beyond electrostatics and deal with time- dependent electromagnetic phenomena Suppose we consider the force between two distant charges q1, q2 in accelerated motion Now the greatest speed with which a signal or information can go from one point to another is c, the speed of light Thus, the effect of any motion of q1 on q2 cannot FIGURE 1
1
474-477
Suppose we consider the force between two distant charges q1, q2 in accelerated motion Now the greatest speed with which a signal or information can go from one point to another is c, the speed of light Thus, the effect of any motion of q1 on q2 cannot FIGURE 1 9 Electric field at a point due to a system of charges is the vector sum of the electric fields at the point due to individual charges
1
475-478
Now the greatest speed with which a signal or information can go from one point to another is c, the speed of light Thus, the effect of any motion of q1 on q2 cannot FIGURE 1 9 Electric field at a point due to a system of charges is the vector sum of the electric fields at the point due to individual charges Rationalised 2023-24 Electric Charges and Fields 17 arise instantaneously
1
476-479
Thus, the effect of any motion of q1 on q2 cannot FIGURE 1 9 Electric field at a point due to a system of charges is the vector sum of the electric fields at the point due to individual charges Rationalised 2023-24 Electric Charges and Fields 17 arise instantaneously There will be some time delay between the effect (force on q2) and the cause (motion of q1)
1
477-480
9 Electric field at a point due to a system of charges is the vector sum of the electric fields at the point due to individual charges Rationalised 2023-24 Electric Charges and Fields 17 arise instantaneously There will be some time delay between the effect (force on q2) and the cause (motion of q1) It is precisely here that the notion of electric field (strictly, electromagnetic field) is natural and very useful
1
478-481
Rationalised 2023-24 Electric Charges and Fields 17 arise instantaneously There will be some time delay between the effect (force on q2) and the cause (motion of q1) It is precisely here that the notion of electric field (strictly, electromagnetic field) is natural and very useful The field picture is this: the accelerated motion of charge q1 produces electromagnetic waves, which then propagate with the speed c, reach q2 and cause a force on q2
1
479-482
There will be some time delay between the effect (force on q2) and the cause (motion of q1) It is precisely here that the notion of electric field (strictly, electromagnetic field) is natural and very useful The field picture is this: the accelerated motion of charge q1 produces electromagnetic waves, which then propagate with the speed c, reach q2 and cause a force on q2 The notion of field elegantly accounts for the time delay
1
480-483
It is precisely here that the notion of electric field (strictly, electromagnetic field) is natural and very useful The field picture is this: the accelerated motion of charge q1 produces electromagnetic waves, which then propagate with the speed c, reach q2 and cause a force on q2 The notion of field elegantly accounts for the time delay Thus, even though electric and magnetic fields can be detected only by their effects (forces) on charges, they are regarded as physical entities, not merely mathematical constructs
1
481-484
The field picture is this: the accelerated motion of charge q1 produces electromagnetic waves, which then propagate with the speed c, reach q2 and cause a force on q2 The notion of field elegantly accounts for the time delay Thus, even though electric and magnetic fields can be detected only by their effects (forces) on charges, they are regarded as physical entities, not merely mathematical constructs They have an independent dynamics of their own, i
1
482-485
The notion of field elegantly accounts for the time delay Thus, even though electric and magnetic fields can be detected only by their effects (forces) on charges, they are regarded as physical entities, not merely mathematical constructs They have an independent dynamics of their own, i e
1
483-486
Thus, even though electric and magnetic fields can be detected only by their effects (forces) on charges, they are regarded as physical entities, not merely mathematical constructs They have an independent dynamics of their own, i e , they evolve according to laws of their own
1
484-487
They have an independent dynamics of their own, i e , they evolve according to laws of their own They can also transport energy
1
485-488
e , they evolve according to laws of their own They can also transport energy Thus, a source of time- dependent electromagnetic fields, turned on for a short interval of time and then switched off, leaves behind propagating electromagnetic fields transporting energy
1
486-489
, they evolve according to laws of their own They can also transport energy Thus, a source of time- dependent electromagnetic fields, turned on for a short interval of time and then switched off, leaves behind propagating electromagnetic fields transporting energy The concept of field was first introduced by Faraday and is now among the central concepts in physics
1
487-490
They can also transport energy Thus, a source of time- dependent electromagnetic fields, turned on for a short interval of time and then switched off, leaves behind propagating electromagnetic fields transporting energy The concept of field was first introduced by Faraday and is now among the central concepts in physics Example 1
1
488-491
Thus, a source of time- dependent electromagnetic fields, turned on for a short interval of time and then switched off, leaves behind propagating electromagnetic fields transporting energy The concept of field was first introduced by Faraday and is now among the central concepts in physics Example 1 7 An electron falls through a distance of 1
1
489-492
The concept of field was first introduced by Faraday and is now among the central concepts in physics Example 1 7 An electron falls through a distance of 1 5 cm in a uniform electric field of magnitude 2