Chapter 23 Wave Optics

In Young's two-slit experiment, a source of green light is used. The separation of fringes in the interference pattern produced can be increased by increasing

• the distance between the screen and the slit

• the size of every slit

• the distance between the two slits

• the intensity of the green light

The figure shows the diffraction pattern by a single slit which have a slit size of 0.017 mm and is placed 80 cm from the screen. The light used has a wavelength of 600 nm. What is the width of the central bright band?

• 5.65 cm

• 6.65 cm

• 7.21 cm

• 8.34 cm

A diffraction grating with 2400 lines per centimetre is used to produce a diffraction pattern that is recorded by a detector. The first-order fringe is 8.94 cm from central fringe. If the distance between the grating and the detector is 0.625 m, what is the wavelength of the electromagnetic wave used?

• 295 nm

• 590 nm

• 1180 nm

• 1190 nm

A diffraction grating that has 2000 slits per centimetre is used to measure the wavelengths emitted by hydrogen gas. At what angle in the first order spectrum would you expect to find the violet line that has a wavelength of 434 nm?

• $3\degree$

• $5\degree$

• $7\degree$

• $9\degree$

A plane polarized light is passed through a polaroid. The polarisation axis of the polaroid is adjusted until the intensity of the light passing through it is at maximum value

 $I_{\max}$ . Through what angle must the polaroid be rotated so that the intensity of light that passes through it is 35% of  $I_{\max}$  ? 

•  $33.1\degree$  

•  $42.6\degree$  

•  $53.7\degree$  

•  $64.8\degree$  

Two stars are just barely resolved by a telescope with a lens diameter of 0.500 m. Determine the angular separation of the two stars. Assume incident light of wavelength is 500 nm.

• $1.22\times10^{-6}\ rad$

• $2.44\times10^{-6}rad$

• $3.66\times10^{-6}rad$

• $4.88\times10^{-6}rad$

The figure shows monochromatic light of wavelength,  $\lambda$ which is illuminated nearly normal onto a thin soap film of thickness, t and refractive index, n. The optical path difference between the reflected rays from the upper and lower surfaces of the soap film is

•  $\frac{2t}{n}$  

•  $2nt$  

•  $\frac{2t}{n}+\frac{\lambda}{2}$  

•  $2nt+\frac{\lambda}{2}$  

A beam of light which consists of two different wavelength $\lambda_1$ and  $\lambda_2$ , ( $\lambda_1>\lambda_2$  ) is incident normally on a piece of diffraction grating. The second order line for  $\lambda_1$  and the third order line for  $\lambda_2$  overlap. What is the ratio of  $\frac{\lambda_1}{\lambda_2}$  ?

• 1.5

• 2.0

• 2.5

• 3.0

A binary star is observed with a telescope. A coloured filter is used to maximise the resolution. (A filter of a given colour transmits only that colour of light). What colour filter would give the greatest increase in the resolution?

• Blue

• Green

• Yellow

• Red

The Rayleigh criterion for resolving power for a circular aperture is

 $\theta=1.22\ \frac{\lambda}{D}$ . Two sources of radio waves are at a distance of 1 $\times10^{12}$ m from the Earth. The sources are separated by 2 $\times10^9$ m and emit radio waves of wavelength 0.03 m. What is the estimate for the diameter of a dish of a radio telescope on the Earth that will just resolve the two sources?

•  $4\times10^{-5}m$  

•  $4\times10^{-4}m$  

• 0.018 m

• 18 m