When a certain metallic surface is illuminated with monochromatic light of wavelength $$\lambda$$, the stopping potential for photoelectric current is $$3V_0$$ and when the same surface is illuminated with light of wavelength $$2\lambda$$, the stopping potential is $$V_0$$. The threshold wavelength of this surface for photoelectric effect is

1) $$6\lambda$$
2) $$4\lambda /3$$
3) $$4\lambda$$
4) $$8\lambda$$

Charges Q, 2Q and 4Q are uniformly distributed in three dielectric solid spheres 1,2 and 3 of radii R/2,R and 2R respectively. If magnitudes of the electric fields at point P at a distance R from the centre of sphere 1, 2 and 3 are E1, E2 and E3 respectively, then :

1) E1>E2>E3
2) E3>E1>E2
3) E2>E1>E3
4) E3>E2>E1

A force of 7N, making an angle q with the horizantal, acting on an object displaces it by 0.5m along the horizontal direction. If the object gains kinetic energy of 2J, what is the horizontal component of the force?

1) 2N
2) 4N.
3) 1N
4) 14N

n identical mercury droplets charged to the same potential V coalesce to form a single bigger drop. The potential of the new drop =

 1) nn

 2) n^2/3 n

 3) n/n

 4) n^1/3 n

What is the magnitude of a point charge which produces an electric field of 2N/C at a distance of 60cm? (1/4πε0=9×10⁹Nm²/C²)

1) 8×10⁻¹¹ coulomb
2) 2×10⁻¹¹ coulomb
3) 3×10⁻¹¹??????? coulomb
4) 6×10⁻¹¹??????? coulomb

The electric field for an electromagnetic wave in free space is $$\vec{E}=\vec{i}30\cos(kz-5\times 10^8t)$$, where magnitude of $$\vec E$$ is in $$V/m$$. The magnitude of wave vector, $$k$$ is:

1) $$0.46$$ $$rad\ m^{-1}$$
2) $$3$$ $$rad\ m^{-1}$$
3) $$1.66$$ $$rad\ m^{-1}$$
4) $$0.83$$ $$rad\ m^{-1}$$

Block of mass 4 kg rests on a rough inclined plane making an angle of 30 with the horizontal. The coefficient of static friction between the block and the plane is 0.7. The friction force on the block is:
1. 9.8 N
2. 13.5 N
3. 16.8 N
4.19.6 N

Two conducting rings of radii r and 2r move in opposite directions with velocities 2v and v respectively on a conducting surface S. There is a uniform magnetic field of magnitude Bperpendicular to the plane of the rings. The potential difference between the highest points of the two rings is

1) zero
2) 2rvB
3) 4rvB
4) 8rvB

In terms of Rydberg constant R, the shortest wavelength in Balmer series of hydrogen atom spectrum will have wavelength:

(1) 3/2 R
(2) 9/4 R
(3) 1/R
(4) 4/R

The capacity of a parallel plate air capacitor is 2μF and voltage between the plates is changing at the rate of 3V/S. The displacement current in the capacitor is:

1) 2μF
2) 3μF
3) 5μF
4) 6μF