Magnetism And Matter — Physics STD 12 Science — Question

The radiant energy of the sun results from:

The correct equation of nuclear fusion reaction is:

An electron initially at rest, is accelerated through a potential difference of 200 volt, so that it acquires a velocity 8.4 . The value of e/m of electron will be

(a) 2.76

(b) 1.76

(c) 0.76

(d) None of these

Let p and E denote the linear momentum and energy of a photon. If the wavelength is decreased:

1. Both p and E increase.
2. P increases and E decreases.
3. P decreases and E increases.
4. Both p and E decrease.

A circular current loop of magnetic moment M is in an arbitrary orientation in an external magnetic field B. The work done to rotate the loop by 30° about an axis perpendicular to its plane is:

An electric bulb marked 40 W - 200 V is used in a circuit of supply voltage 100 V. Now its power is:

Figure shows a charge q placed at the centre of a hemisphere. A second charge Q is placed at one of the positions A, B, C and D. In which position(s) of this second charge, the flux of the electric field through the hemisphere remains unchanged?

1. A
2. B
3. C
4. D

Assertion :   We can measure the potential barrier of a PN junction by putting a sensitive voltmeter across its terminals.

Reason     : The current through the PN junction is not same in forward and reversed bias.

(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 assertion is false but reason is true.

Identify the wrong statement describing the color code for carbon resistors.

Two metallic plates A and B, each of area 5 ´ 10^–4m² are placed parallel to each other at a separation of 1 cm. Plate B carries a positive charge of 33.7 pc. A monochromatic beam of light, with photons of energy 5 eV each, starts falling on plate A at t = 0, so that 10¹⁶ photons fall on it per square meter per second. Assume that one photoelectron is emitted for every 10⁶ incident photons. Also assume that all the emitted photoelectrons are collected by plate B and the work function of plate A remains constant at the value 2 eV. Electric field between the plates at the end of 10 seconds is

(a) 2 × 103 N/C

(b) 103 N/C

(c) 5 × 103 N/C

(d) Zero