Ex.9.1
3. A light meter registers a value of 100 W m-2 when placed at a distance of 50 cm from a small bright light in a dark room.
a) What value will it register at a distance of 150 cm from the same source? (2)
b) What value will it register at a distance of 25 cm from the same source? (2)
Ex.9.2
6. Calculate the energy of a photon of light of wavelength 405 nm. (2)
7. Calculate the wavelength of a photon of energy 4.2 x 10-19 J. (2)
10. The work function for sodium metal is 2.9 x 10-19 J.
Light of wavelength 5.4 x 10-7 m strikes the surface of this metal.
What is the maximum kinetic energy of the electrons emitted from the surface? (3)
Ex.9.3
2.
The diagram shows the energy levels for the hydrogen atom.
a) Between which two energy levels would an electron transition lead to emission of radiation of highest frequency? (1)
b) Calculate the frequency of this radiation. (3)
Ex.9.4
1. The emission spectrum of helium contains only a few sharp lines of light in certain colours.
Explain how these lines are produced. (2)
11.
A Bunsen flame containing vaporised sodium is placed between a sodium vapour lamp and a screen.
a) Explain why the flame casts a dark shadow. (2)
b) The sodium lamp is now replaced with a cadmium lamp.
Explain why there is no longer a dark shadow on the screen. (2)
Past Papers
3.
A student directs a ray of monochromatic light through a semicircular glass block.
At point X the incident ray splits into two rays:
T - a transmitted ray and
R - a reflected ray.
The student uses a light meter to measure the irradiance of ray R as angle θ is changed.
(a) State what is meant by the irradiance of a radiation. (1)
(b) Explain why, as angle θ is changed, it is important to keep the light meter at a constant distance from point X for each measurement of intensity. (1)
(c) The graph below is obtained from the student's results.
graph.
(i) What is the value of the critical angle in the glass for this light? (1)
(ii) Calculate the refractive index of the glass for this light. (2)
(iii) As the angle θ is increased, what happens to the intensity of ray T? (1)
4.
The apparatus shown is used to investigate photoelectric emission from a metal surface.
The irradiance and frequency of the incident radiation can be varied as required.
(a) (i) Explain what is meant by photoelectric emission from a metal. (2)
(ii) What name is given to the minimum frequency of the radiation that produces a current in the circuit? (1)
(iii) A particular source of radiation produces a current in the circuit.
Explain why the current increases as the irradiance of the radiation increases. (1)
(b) A semiconductor chip is used to store information. The information can only be erased by exposing the chip to ultraviolet radiation for a period of time.
The following data is provided:
Frequency of ultraviolet radiation used = 9.0 x 1014 Hz
Minimum irradiance of UV required at chip = 25 W m-2
Area of chip exposed to radiation = 1.8 x 10-9 m2
Time taken to erase the information = 15 minutes
Energy of radiation needed to erase the information = 40.5 µJ
(i) Calculate the energy of a photon of the ultraviolet radiation used. (2)
(ii) Calculate the number of photons of the ultraviolet radiation required to erase the information. (2)
(iii) Sunlight of irradiance 25 W m-2, at the chip, can also be used to erase the information.
State whether the time taken to erase the information is greater than, equal to or less than 15 minutes.
You must justify your answer. (1)
Total marks = (36)