Semiconductor Electronic: Material, Devices And Simple Circuits — Physics STD 12 Science — Question

The 21 cm radio wave emitted by hydrogen in interstellar space is due to the interaction called the hyperfine interaction is atomic hydrogen. the energy of the emitted wave is nearly

(a)  Joule

(b) 1 Joule

(c) 7  Joule

(d)  Joule

 The resistivity of certain metals or alloys drops to zero when they are cooled below a certain temperature, this phenomenon is known as __________.

A block of mass M is hanging over a smooth and light pulley through a light string. T he other end of the string is pulled by a constant force F. The kinetic energy of the block increases by 20J in 1s.

1. The tension in the string is Mg.
2. The tension in the string is F.
3. The work one by the tension on the block is 20J in the above 1s.
4. The work done by the force of gravity is -20J in the above 1s.

Six charges, three positive and three negative of equal magnitude are to be placed at the vertices of a regular hexagon such that the electric field at O is double the electric field when only one positive charge of same magnitude is placed at R. Which of the following arrangements of charges is possible for P, Q, R, S, T and U respectively

(a) +, -, +, -, -, +

(b) +, -, +, -, +, -

(c) +, +, -, +, -, -

(d) -, +, +, -, +, -

Which of the following is the fusion reaction

(a)	(b)
(c)	(d)

Under which of the following conditions will a convex mirror of focal length f produce an image that is erect, diminished and virtual

(a) Only when 2f  > u > f	(b) Only when u = f
(c) Only when u < f	(d) Always

The significant result deduced from the Rutherford's scattering experiment is that:

An ac generator consists of a coil of 200 turns, 100cm in diameter. If the coil rotates at 500 rpm in a magnetic field of 0.25T, then the maximum induced emf.

A 3volt battery with negligible internal resistance is connected in a circuit as shown in the figure.  The current I, in the circuit will be

(a) 1/3 A

(b) 1 A

(c) 1.5 A

(d) 2 A