Magnetism And Matter — Physics STD 12 Science — Question

Assertion  :  The drift velocity of electrons in a metallic wire will decrease, if the temperature of the wire is increased.

Reason      : On increasing temperature, conductivity of metallic wire decreases.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If the assertion and reason both are false.

When half of a lens is wrapped in a black cloth, what will be the effect on the image formed by the lens?

A diode, a resistor and a 50Hz AC source are connected in series. The number of current pulses per second through the resistor is:

Permanent magnets should have:

A uniform wire is bent in the form of a circle of radius R. A current I enters at A and leaves at C as shown in the figure :

If the length ABC is half of the length ADC, the magnetic field at the centre O will be

(a) Zero

(b)

(c)

(d)

A double convex thin lens made of glass (refractive index  μ = 1.5) has both radii of curvature of magnitude 20 cm. Incident light rays parallel to the axis of the lens will converge at a distance L such that

(a) L = 20 cm

(b) L = 10 cm

(c) L = 40 cm

(d) L = 20 / 3 cm

A constant voltage is applied between the two ends of a metallic wire. If both the length and the radius of the wire are doubled, the rate of heat developed in the wire

(a) Will be doubled	(b) Will be halved
(c) Will remain the same	(d) Will be quadrupled

The percentage of mass lost during nuclear fusion is:

Two rays A and B being reflected by a mirror and going as A' and B'. The mirror:

1. Is plane.
2. Is convex.
3. Is concave.
4. May be any spherical mirror.

In Young's double slit experiment, if the two slits are illuminated with separate sources, no interference pattern is observed because

(a) There will be no constant phase difference between the two waves

(b) The wavelengths are not equal

(c) The amplitudes are not equal

(d) None of the above