Waves and particle nature of lightEdexcel A-Level Physics: Topic test

20 questions, 54 marks

Edexcel A-Level Physics

Waves and particle nature of light topic test

Total 54 marks

Name

Class

Date

1
A wave travels across the open sea with wavelength 64 m and period 8.0 s. A small cork floats on the surface and moves up and down as the wave passes.
(a)
What is the speed of the wave?
[1 mark]
A0.13 m s⁻¹
B8.0 m s⁻¹
C510 m s⁻¹
D4.0 m s⁻¹
(b)
Two corks are 16 m apart along the direction in which the wave travels. What is the phase difference between their motions?
[1 mark]
A0
Bπ rad
Cπ/4 rad
Dπ/2 rad
(c)
Calculate the frequency of the wave and the time a cork takes to move from a crest position to the next trough position.
[2 marks]
Total for question 1: 4 marks
2
A laser emits a narrow beam of light of power 5.0 mW and diameter 2.0 mm.
(a)
What is the intensity of the beam?
[1 mark]
A1.6 × 10³ W m⁻²
B4.0 × 10² W m⁻²
C6.3 × 10⁻⁴ W m⁻²
D1.3 × 10³ W m⁻²
(b)
The beam is plane polarised. Which of these waves can also be plane polarised?
[1 mark]
ASound waves in air
BUltrasound in soft tissue
CRadio waves
DA longitudinal pulse on a spring
(c)
A lens spreads the beam, with its power unchanged, so that its diameter doubles. Calculate the new intensity.
[2 marks]
Total for question 2: 4 marks
3
A microwave transmitter of frequency 9.4 GHz is directed at a flat metal sheet, which reflects the waves straight back. A small detector is moved along the line between the transmitter and the sheet. It finds positions of minimum signal that are 1.6 cm apart.
(a)
Explain how the minima arise and why adjacent minima are half a wavelength apart.
[3 marks]
(b)
Calculate the speed of the microwaves from these measurements. The transmitter is then replaced by one that gives minima 1.2 cm apart; calculate its frequency.
[4 marks]
Total for question 3: 7 marks
4
A green laser emits light of wavelength 532 nm and power 5.0 mW. Its beam is directed at normal incidence onto a diffraction grating with 400 lines per millimetre, forming a pattern of bright spots on a distant screen. The beam is then directed onto a clean metal surface of work function 2.0 eV. Planck constant h = 6.63 × 10⁻³⁴ J s, speed of light c = 3.00 × 10⁸ m s⁻¹, e = 1.60 × 10⁻¹⁹ C.
(a)
Determine the number of bright spots on the screen, including the central one, and the angle of the outermost spot to the straight-through direction. Explain why the spots appear.
[6 marks]
(b)
Calculate the energy of a photon of the laser light in eV and the maximum kinetic energy of the photoelectrons, and the number of photons reaching the metal each second. Explain what happens to the photoelectrons if the laser intensity is doubled.
[6 marks]
Total for question 4: 12 marks
5
Light in air strikes the flat surface of a diamond of refractive index 2.42 at an angle of incidence of 50° to the normal. Some of the light that enters the diamond later meets a diamond-air boundary from inside.
(a)
What is the angle of refraction in the diamond?
[1 mark]
A21°
B50°
C18°
D24°
(b)
What is the critical angle for a diamond-air boundary?
[1 mark]
A24°
B66°
C0.41°
D42°
(c)
State the two conditions needed for total internal reflection at a boundary.
[2 marks]
Total for question 5: 4 marks
6
A thin converging lens has a power of +8.0 D. A small illuminated object 3.0 cm tall is placed 0.50 m from the lens, on its principal axis.
(a)
What is the focal length of the lens?
[1 mark]
A8.0 m
B0.80 m
C0.25 m
D0.125 m
(b)
What is the distance of the image from the lens?
[1 mark]
A0.63 m
B0.17 m
C0.10 m
D6.0 m
(c)
Calculate the magnification and the height of the image.
[2 marks]
Total for question 6: 4 marks
7
A beam of thermal neutrons, each with kinetic energy 0.025 eV and mass 1.67 × 10⁻²⁷ kg, is directed at a crystal in which the spacing between planes of atoms is about 0.20 nm. Planck constant h = 6.63 × 10⁻³⁴ J s, e = 1.60 × 10⁻¹⁹ C.
(a)
Calculate the de Broglie wavelength of the neutrons.
[3 marks]
(b)
Explain why these neutrons give a clear diffraction pattern with the crystal, and show that electrons with the same kinetic energy would not.
[4 marks]
Total for question 7: 7 marks
8
A lamp contains atoms of a gas whose lowest three energy levels are −9.0 eV (ground state), −4.5 eV and −2.0 eV. The lamp emits light by transitions between these three levels only. Visible light has frequencies between 4.0 × 10¹⁴ Hz and 7.5 × 10¹⁴ Hz. Planck constant h = 6.63 × 10⁻³⁴ J s, e = 1.60 × 10⁻¹⁹ C. Radiation from the lamp is directed at a clean metal surface of work function 5.0 eV.
(a)
Calculate the frequencies of the lines the lamp can emit and explain why only certain frequencies are emitted. State which line is visible.
[6 marks]
(b)
Determine which lines can cause photoelectric emission from the metal, calculate the maximum kinetic energy of the photoelectrons and the threshold frequency, and explain why increasing the lamp's intensity cannot make the 4.5 eV line eject electrons.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).