Question 1

In a Young's double-slit experiment,what happens to the angular separation between the fringes when the wavelength is increased at the same time that the slit separation is decreased?

Accepted Answer

The angular separation between the fringes in a Young's double-slit experiment is given by the formula θ = λ/d, where λ is the wavelength of light and d is the distance between the slits. Increasing the wavelength (λ) while decreasing the slit separation (d) both contribute to increasing the angular separation (θ), hence the angular separation between the fringes increases.

Question 2

LCD stands for:

Accepted Answer

LCD stands for "liquid crystal display", which is a type of technology used in electronic screens such as televisions, computer monitors, and mobile devices. Options A, B, and D do not accurately describe LCD technology.

Question 3

In a Young's double-slit experiment,both the wavelength and the slit separation are increased by 50%.What happens to the distance between two adjacent bright fringes?

Accepted Answer

The distance between two adjacent bright fringes in a Young's double-slit experiment is given by the formula D = λL/d, where λ is the wavelength of the light, L is the distance between the slits and the screen, and d is the slit separation.

If both the wavelength and the slit separation are increased by 50%, then the new distance between two adjacent bright fringes will be:

D' = (1.5λ) / (1.5d) * L = λ/d * L = D

Therefore, the distance stays the same.

Question 4

A Young's double-slit experiment is performed in air and then the apparatus is submerged in water.What happens to the fringe separation,and what can be used to explain the change,if any?

Accepted Answer

When light passes from air to water, its wavelength decreases while its frequency remains constant. This is known as the phenomenon of refraction. As the wavelength decreases, the fringe separation also decreases. Therefore, the correct choice is D.

Question 5

Light travels from outside a building to inside through a pane of glass.Which of the following is true regarding the phase change upon reflection in the case?

Accepted Answer

When light travels from a medium of lower refractive index (air) to a medium of higher refractive index (glass), a 180-degree phase change occurs upon reflection at the boundary (outside surface of the glass). However, when light reflects off the inside surface (glass to air), there is no phase change because it is moving from a higher to a lower refractive index medium.

Question 6

Plane polarized light is sent through two consecutive polarizers,the first having its plane of polarization in the same direction as the incident light and the second having its plane at 90 $\degree$ to the original plane of polarization.A third polarizer,with plane of polarization at 30 $\degree$to the original plane of polarization,is placed between the two other polarizers.What fraction of the original intensity now gets through?

Accepted Answer

When plane polarized light passes through the first polarizer, the intensity remains the same. Now, the second polarizer is oriented perpendicular to the original plane of polarization, so the intensity drops to zero because all the light is now polarized perpendicular to the transmission axis of the second polarizer.

When the third polarizer is introduced between the two other polarizers, it only allows  cos^2(30°) = 0.75  of the light through because the angle between its transmission axis and the plane of polarization is 30°.

Therefore, the fraction of the original intensity that gets through is:
I_final/I_initial = 0.75 x 0 = 0 
So the answer is D.

Question 7

Diffraction grating #1 has half the lines/cm that diffraction grating #2 does.When used with a certain wavelength of light,both gratings give first order maxima.Which of the following statements is true for the same wavelength of light.

Accepted Answer

The answer of Diffraction grating #1 has half the lines/cm...

Question 8

A beam of plane polarized light is incident on 3 polarizers,the first with an axis at 30 $\degree$to the original plane of polarization,the second at 60 $\degree$ to the original plane of polarization,and the third at 90 $\degree$to the original plane of polarization.What angle does the plane of polarization of the transmitted light make with the original plane of polarization of the original beam?

Accepted Answer

Each polarizer will block any component of the light that is perpendicular to its axis, so as the light passes through the three polarizers, only the component that is parallel to the axis of the third polarizer will be transmitted. Since the axis of the third polarizer is perpendicular to the original plane of polarization, the transmitted light will be polarized in the plane perpendicular to the original plane, which is 90° to the original plane. Therefore, the answer is (B) 90°.

Quiz 24: Wave Optics