The box of a pinhole camera, of length L, has a hole of radius a. It is assumed that when the hole is illuminated by a parallel beam of light of wavelength λ the spread of the spot (obtained on the opposite wall of the camera) is the sum of its geometrical spread and the spread due to diffraction. The spot would then have its minimum size (say b_min) when:

2.

Radiation of wavelength λ is incident on a photocell. The fastest emitted electron has to speed v. If the wavelength is changed to 3λ/4, the speed of the fastest emitted electron will be:

• 
• 

•  = v(4/3)^1/2

•  = v(4/3)^1/2

A green light is an incident from the water to the air – water interface at the critical angle (θ). Select the correct statement

• The entire spectrum of visible light will come out of the water at various angles to the normal.

• The spectrum of visible light whose frequency is less than that of green light will come out to the air medium

• The spectrum of visible light whose frequency is more than that of green light will come out to the air medium.

• The spectrum of visible light whose frequency is more than that of green light will come out to the air medium.

Two beams, A and B, of plane polarised light with mutually perpendicular planes of polarisation are seen through a Polaroid. From the position when the beam A has maximum intensity (and beam B has zero intensity), a rotation of Polaroid through 300 makes the two beams appear equally bright. If the initial intensities of the two beams are IA and IB respectively, then I_A/I_B equals:

• 3

• 3/2

• 1

• 1

A beam of unpolarized light of intensity I₀ is passed through a Polaroid A and then through another polaroid B which is oriented so that its principal plane makes an angle of 45° relative to that of A.The intensity of the emergent light is

• I₀

• I₀/2

• I₀/4

• I₀/4

Two coherent point sources S₁ and S₂ are separated by a small distance ‘d’ as shown. The fringes obtained on the screen will be:

• point

• straight lines

• Semi-circle

• Semi-circle

A cylindrical tube, open at both ends, has a fundamental frequency, f, in the air. The tube is dipped vertically in water so that half of it is in water. The fundamental frequency of the air-column is now

• f

• f/2

• 3f/4

• 3f/4

This question has statement 1 and statement 2. Of the four choices given after the statements, choose the one that best describes the two statements
Statement 1: Davisson – Germer experiment established the wave nature of electrons.
Statement 2: If electrons have wave nature, they can interfere and show diffraction.

• Statement 1 is false, Statement 2 is true

• Statement 1 is true, Statement 2 is false

• Statement 1 is true, Statement 2 is the correct explanation for statement 1

• Statement 1 is true, Statement 2 is the correct explanation for statement 1

In Young's double slit experiment, one of the slit is wider than other, so that the amplitude of the light from one slit is double of that from other slits. If I_m be the maximum intensity, the resultant intensity I when they interfere at phase difference φ is given by

The question has a paragraph followed by two statements, Statement 1 and Statement 2. Of the given four alternatives after the statements, choose the one that describes the statements. A thin air film is formed by putting the convex surface of a plane-convex lens over a plane glass plate. With monochromatic light, this film gives an interference pattern due to light reflected from the top (convex) surface and the bottom (glass plate) surface of the film.

Statement 1 :
When light reflects from the air-glass plate interface, the reflected wave suffers a phase change of π
Statement 2 :
The centre of the interference pattern is dark.

• Statement 1 is true, statement 2 is false. 

• Statement 1 is true, Statement 2 is true, Statement 2 is the correct explanation of Statement 1

• Statement 1 is true, Statement 2 is true, Statement 2 is not the correct explanation of Statement 1

• Statement 1 is true, Statement 2 is true, Statement 2 is not the correct explanation of Statement 1