Two changes +q and -q are attached to the two ends of a light rod of length L, as shown in figure. The system is given a velocity ν perpendicular to magnetic field . The magnetic force on the system of charges and magnitude of force on one charge by the rod, are respectively
zero, zero
zero, qvB
2qvB, 0
2qvB, qvB
The intensity of magnetic field due to an isolated pole of strength mp at a point distant r from it will be
mp/r2
mp r2
r2/ mp
mp/r
A bulb and a condenser are connected in with an A>C source. On increasibg the frequency will
increase
decrease
sometimes increase and sometimes decrease
neither increase nor decrease.
The ratio of magnetic fields on the axis of a circular current carrying coil of radius a to the magnetic field at its centre will be
A.
Consider a circular radius of a, carrying a current I. Consider a point P, which is at a distance x from the centre of coil. We can consider that the loop is made p of a large number of short element, generating small magnetic fields. So the total field at P will be the sum of the contributions of all these elements. At the centre of coil, the field will be uniform.
By Biot- Savart’s law, the field dB due to a small element dl of the circle, centered at A is given by
dB =
This can be resolved into two components, one along the axis OP, and other PS, which is perpendicular to OP. PS is exactly cancelled by the perpendicular component PS’ of the field due to a current and centered at A’. So, the total magnetic field at a point which is at a distance x away from the axis of a circular coil of radius a is given by,
dB =
μ0, I are constants and by divide and multiply by a2 on denominator and numerator we get
dB =
A charge q is uniformly distributed on a ring of radius r. A sphere of an equal radius is constructed with its centre lying on the periphery of the ring. The flux of electric field through the surface of the sphere will be
When 100 V d.c is applied across a coil, a current of 1 A nows through it. When 100 V a.c. of 50 Hz is applied to the same coil only 0.5 A flows. The inductance of the coil is
0.55 H
5.5 H
0.55 mH
55 mH
A bulb of 25 W. 200 V and another bulb of 100 W, 200 V are connected in series with a supply line of 220 V. Then
both bulbs will glow with same brightness
both bulbs will get fused
25 W bulb will glow more brightly
100 W bulb will glow more brightly