Ray Optics and Optical Instruments — Physics STD 12 Science — Question

Which of the following metals is not sensitive to visible light?

Choose the correct statement:

Focal length of a plane mirror is

(a) Zero

(b) Infinite

(c) Very less

(d) Indefinite

Which of the following particles will describe the smallest circle when projected with the same velocity perpendicular to a magnetic field?

One conducting U tube can slide inside another as shown in figure, maintaining electric contacts between the tubes. The magnetic field B is perpendicular to the plane of the figure. If each tube moves towards the other at a constant speed v, then the emf induced in the circuit in terms of B, l and v where l is the width of each tube, will be

A bar magnet is released from rest along the axis of a very long, vertical copper tube. After some time the magnet:

1. Will stop in the tube.
2. Will move with almost content speed.
3. Will move with an acceleration g.
4. Will oscillate.

The AC voltage across a resistance can be measured using:

1. A potentiometer.
2. A hot-wire voltmeter.
3. A moving-coil galvanometer.
4. A moving-magnet galvanometer.

If a 30 V, 90 W bulb is to be worked on a 120 V line, a resistance of how many ohms should be connected in series with the bulb

(a) 10 ohm

(b) 20 ohm

(c) 30 ohm

(d) 40 ohm

At what temperature will the resistance of a copper wire become three times its value at 0 ^oC  (Temperature coefficient of resistance for copper = 4 × 10^–3 per ^oC )

(a)  400 oC

(b)  450 oC

(c)  500 oC

(d)  550 oC