Electromagnetic Waves — Physics STD 12 Science — Question

Which is a wrong statement

(a) The Wheatstone bridge is most sensitive when all the four resistances are of the same order

(b) In a balanced Wheatstone bridge, interchanging the positions of galvanometer and cell affects the balance of the bridge

(c) Kirchhoff's first law (for currents meeting at a junction in an electric circuit) expresses the conservation of charge

(d) The rheostat can be used as a potential divider

Who first discovered the relationship between electricity and magnetism?

The image formed by a convex mirror of focal length 30 cm is a quarter of the size of the object. The distance of the object from the mirror is

(a) 30 cm

(b) 90 cm

(c) 120 cm

(d) 60 cm

Points A and B are situated perpendicular to the axis of a 2cm long bar magnet at large distances X and 3X from its centre on opposite sides. The ratio of the magnetic fields at A and B will be approximately equal to

(a) 1 : 9

(b) 2 : 9

(c) 27 : 1

(d) 9 : 1

In a region of uniform magnetic induction , a circular coil of radius 30 cm and resistance ohm is rotated about an axis which is perpendicular to the direction of B and which forms a diameter of the coil. If the coil rotates at 200 rpm the amplitude of the alternating current induced in the coil is

(a) mA

(b) 30 mA

(c) 6 mA

(d) 200 mA

An alternating current of frequency 200 rad/sec and peak value 1A as shown in the figure, is applied to the primary of a transformer. If the coefficient of mutual induction between the primary and the secondary is 1.5 H, the voltage induced in the secondary will be

(a) 300 V

(b) 191 V

(c) 220 V

(d) 471 V

A long straight horizontal cable carries a current of 2.5 A in the direction 10° south of west to 10° north of east. The magnetic meridian of the place happens to be 10° west of the geographic meridian. The earth’s magnetic field at the location is 0.33 Gauss, and the angle of dip is zero. Locate the line of neutral points. (Ignore the thickness of the cable).

A rod of a certain metal is 1.0 m long and 0.6 cm in diameter.  Its resistance is 3.0 ×   ohm.  Another disc made of the same metal is 2.0 cm in diameter and 1.0 mm thick.  What is the resistance between the round faces of the disc

(a) 1.35 ×   ohm

(b) 2.70 ×   ohm

(c) 4.05 ×   ohm

(d) 8.10 ×   ohm

How much water should be filled in a container 21 cm in height, so that it appears half filled when viewed from the top of the container  (given that a = 4/3)

(a) 8.0 cm

(b) 10.5 cm

(c) 12.0 cm

(d) None of the above

Magnitude of potential difference across L. C and R in a series LCR circuit is 100 V. If resistor is re- moved, then magnitude of current in the circuit is: