Download Irradiance and photoelectric effect hw

Irradiance and photoelectric effect hw
1) A student carried out an experiment to investigate how irradiance
varies with distance from a small lamp. The following results were
obtained.
Distance from source / m
0·20
0·30
0·40
0·50
Irradiance / units
675
302
170
108
a) What is meant by the term irradiance?
b) Use all the data to find the relationship between irradiance I and the
distance d from the source.
2) A light bulb at a distance of 4m from a desk produces an irradiance of
0·8Wm-2 at the desk.
a) If the bulb is brought to a distance of 1m from the desk, what is the
irradiance?
b) What irradiance is produced at the desk when the bulb is 6m away?
c) If the desk is 2m long and 0·8m wide, how long does it take for 100J
of light energy to fall on it when the bulb is at a distance of 2m?
3) The apparatus shown below is used to investigate photoelectric
emission from a metal surface.
incident
metal
radiation
surface
A
-
constant voltage
supply
+
a) Explain what is meant by photoelectric emission from a metal.
b) What is the name given to the minimum frequency of the radiation that
produces a current in the circuit?
c) A particular source of radiation produces a current in the circuit.
Explain why the current in the circuit increases as the irradiance of the
radiation is increased.
4) Ultraviolet radiation has a frequency of 1·2 × 1015Hz.
a) Calculate the energy of a photon of this light.
( Plank’s constant is 6·63 × 10-34Js )
b) This light is to be used to deliver 20µJ of energy to a surface. How
many photons are required to do this?
c) The ultraviolet light source is replaced by white light. In order to
supply the same amount of energy as the ultraviolet source, will the
number of photons from the white light source be more, the same or
fewer? Explain your answer.
5) A scientist who wants to produce the photoelectric effect in a piece of
metal has a choice of red, green or blue light sources. She finds that
only one of the sources can cause the photoelectric effect. Say which
one it is and explain why?
Irradiance and photoelectric effect hw
1) A student carried out an experiment to investigate how irradiance
varies with distance from a small lamp. The following results were
obtained.
Distance from source / m
0·20
0·30
0·40
0·50
Irradiance / units
675
302
170
108
a) What is meant by the term irradiance?
b) Use all the data to find the relationship between irradiance I and the
distance d from the source.
2) A light bulb at a distance of 4m from a desk produces an irradiance of
0·8Wm-2 at the desk.
a) If the bulb is brought to a distance of 1m from the desk, what is the
irradiance?
b) What irradiance is produced at the desk when the bulb is 6m away?
c) If the desk is 2m long and 0·8m wide, how long does it take for 100J
of light energy to fall on it when the bulb is at a distance of 2m?
3) The apparatus shown below is used to investigate photoelectric
emission from a metal surface.
incident
metal
radiation
surface
A
-
constant voltage
supply
+
a) Explain what is meant by photoelectric emission from a metal.
b) What is the name given to the minimum frequency of the radiation that
produces a current in the circuit?
c) A particular source of radiation produces a current in the circuit.
Explain why the current in the circuit increases as the irradiance of the
radiation is increased.
4) Ultraviolet radiation has a frequency of 1·2 × 1015Hz.
a) Calculate the energy of a photon of this light.
( Plank’s constant is 6·63 × 10-34Js )
b) This light is to be used to deliver 20µJ of energy to a surface. How
many photons are required to do this?
c) The ultraviolet light source is replaced by white light. In order to
supply the same amount of energy as the ultraviolet source, will the
number of photons from the white light source be more, the same or
fewer? Explain your answer.
5) A scientist who wants to produce the photoelectric effect in a piece of
metal has a choice of red, green or blue light sources. She finds that
only one of the sources can cause the photoelectric effect. Say which
one it is and explain why?