When two magnetic moments are compared using equal distance method the deflections produced are 45o and 30o. If the length of magnets are in the ratio 1 : 2, the ratio of their pole strengths is
|
(a) 3 : 1 |
(b) 3 : 2 |
(c) |
(d) 2 |
(d) 2
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A magnet of magnetic moment M oscillating freely in earth's horizontal magnetic field makes n oscillations per minute. If the magnetic moment is quadrupled and the earth's field is doubled, the number of oscillations made per minute would be
(a) 
|
(b) 
|
(c) 2
|
(d)
|
A rectangular coil of 300 turns has an average area of average area of 25 cm × 10 cm. The coil rotates with a speed of 50 cps in a uniform magnetic field of strength 4 
about an axis perpendicular of the field. The peak value of the induced e.m.f. is (in volt)
|
(a) 3000 π |
(b) 300 π |
(c) 30 π |
(d) 3 π |
An electric wire of length ‘I’ and area of cross-section a has a resistance R ohms. Another wire of the same material having same length and area of cross-section 4a has a resistance of
|
(a) 4R |
(b) R/4 |
(c) R/16 |
(d) 16R |
A non-conducting solid sphere of radius R is uniformly charged. The magnitude of the electric field due to the sphere at a distance r from its centre
|
(a) Increases as r increases for r < R |
(b) Decreases as r increases for 0 < r < ∞ |
|
(c) Decreases as r increases for R < r < ∞ |
(d) a, c |