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

Two wires have resistance of 2W and 4W connected to same voltage, ratio of heat dissipated at resistance is

(a) 1 : 2

(b) 4 : 3

(c) 2 : 1

(d) 5 : 2

A double star is a system of two stars rotating about their centre of mass only under their mutual gravitational attraction. Let the star have mass m and 2m and their separation be l. Their time period of rotation about their centre of mass will be proportional to

(a)

(b) l

(c)

(d)

The temperature of a solid object is observed to be constant during a period. In this period:

1. Heat may have been supplied to the body.
2. Heat may have been extracted from the body.
3. No heat is supplied to the body.
4. No heat ia ertracted from the body.

Which of the nine planets is nearest to sun

(a) Venus

(b) Mercury

(c) Mars

(d) Jupiter

Photo-electric effect can be explained by

(a) Corpusular theory of light	(b) Wave nature of light
(c) Bohr’s theory	(d) Quantum theory of light

A horizontal circular loop carries a current that looks clockwise when viewed from above. It is replaced by an equivalent magnetic dipole consisting of a south pole S and a north pole N:

Three observers A, B and C measure the speed of light coming from a source to be  and . The observer A moves towards the source, the observer C moves away from the source with the same speed. The observer B stays stationary. the surrounding space is vacuum every where. Then

(a)

(b)

(c)

(d)

Which of the following transitions in a hydrogen atom emits photon of the highest frequency

(a) n = 1 to n = 2

(b) n = 2 to n = 1

(c) n = 2 to n = 6

(d) n = 6 to n = 2

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.

A moving coil sensitive galvanometer gives at once much more deflection. To control its speed of deflection

(a) A high resistance is to be connected across its terminals

(b) A magnet should be placed near the coil

(c) A small copper wire should be connected across its terminals

(d) The body of galvanometer should be earthed