Page 5 - English Class X_cbse new (FINAL).cdr

TOPIC - 1

Electric field

Sub Topic: 1.2

QUESTION SOLUTION Marking TIPS & EXPLANATION
(a) Derive an expression for the electric field E (a) Scheme
Tips:
due to a dipole of length '2a' at a point distant [1]
(a) F
qo
r from the centre of the dipole on the axial Electric field can be given by E = q ⋅qo
r2
line. Where F is force between two charges F= 1
4πεo
(b) Draw a graph of E versus r for r >> a.
(c) if this dipole were kept in a uniform external Electric field on point P due to charge + q
q
electric field Eo, diagrammatically repre- E1 = 1 (r
sent the position of the dipole in stable and 4πεo − a)2

unstable equilibrium and write the expression Electric field on point P due to charge – q
−q
for the torque acting on the dipole in both the E2 = 1
cases. 4πεo (r + a)2

[5] OD Set-2 [2017] = −1 q
4πεo
(r + a)2

Net electric field, Enet = E1 + E2

q °­ 1 1 ½° [1]
4SHo ® ¾ [½]
°¯ r a 2 r a2 ¿°

S2 a2 2Sa r 2 a2 2ra

(S a)2 (S a)2

q 4ra

4SHo r 2 a2 2

1 2pr
4SHo r 2 a2 2
Enet

if r !! a

Enet 2kPr 2kP
r4 r3

Physics Booklet_Unit 1_.indd 3 3

8/17/2018 8:35:14 AM