The amount of charge Q passed in time t through a cross-section of a wire is Q = 5t2 + 3t + 1. The value of current at time t = 5 s is
9 A
49 A
53 A
none of these
Three charges each of +1?C are placed at the corners of an equilateral triangle. If the force between any two charges be F, then the net force on either charge will be
2 F
3 F
Given that q1 + q2 = q. For what ratio q1/q will the force between q1 and q2 be maximum?
0.25
0.5
1
2
An insulated sphere of radius R has charge density ?. The electric field at a distance r from the centre of the sphere (r < R)
Two point charges +3?C and +8?C repel each other with a force of 40 N. If a charge of –5?C is added to each of them, then the force between them will become
–10 N
+10 N
+20 N
–20 N
Two point charges exert on each other a force F when they are placed r distance apart in air. When they are placed R distance apart in a medium of dielectric constant K, they exert the same force. The distance R equals:
r K
Two conducting spheres of radii r1 and r2 are at the same potential. The ratio of the their charges is
r1/r2
r2/r1
Two conducting spheres of radii r1 and r2 are equally charged. The ratio of their potential is
r1/r2
r2/r1
An electron of mass ‘m’ and charge ‘e’ is accelerated from rest through a potential difference ‘V’ in vacuum. Its final speed will be
eV / 2m
eV/m
A large insulated sphere of radius ‘r’ charged with ‘Q’ units of electricity is placed in contact with a small insulated sphere of radius r' and is then separated. The charge on smaller sphere will now be
Q (r + r)
Q (r + r')
The electric potential V is given as a function of distance x (metre) by V = (5x2 + 10x – 4) volt. Value of electric field at x = 1 m is
–23 V/m
11 V/m
6 V/m
–20 V/m
A straight wire of length l and electric dipole moment p is bent to form a semicircle. The new dipole moment would be
p/2
p/2?
2p
Q, 2Q
C
2 C
3 C
4 C
10(
20(
30(
40(