Download Data Analysis Exercise

Light and Matter: Data Analysis Exercise (modified)
What you will be expected to be able to do:
To explain:
 the Photoelectric Effect
 the motion of electric charges in an electric field
To:
 calculate the size of an electric field between parallel plates
 calculate the size of an electric force on an electric charge
 calculate an electron’s speed and kinetic energy when accelerated by an electric field
 convert energy values between the units of electron volts and joules
 use the relationship ‘EKmax = hf – W’ to calculate the Work Function, Planck’s Constant and the
Threshold Frequency
To:
 plot data in a graph
 analyse and interpret a graph, including error analysis
Data:
Speed of Light
Mass of electron
Charge on electron
Planck’s constant
Formula
Energy change of electrons: E = Vq
Energy of photons: EP = hf
Photoelectric Effect: EKmax = hf - W
Kinetic Energy: EK = ½mv2
Work: W= Fx = EK
c = 3.0 x 108 m/s
me = 9.1 x 10-31 kg
qe = 1.6 x 10-19 C
h = 6.63 x 10-34 J.s
h = 4.1 x 10-15 eV.s
-
- - - -
Light
A
V
+ + +
+
Plate separation = 0.60 cm
Light of a set frequency is shone onto a plate of Sodium. Electrons are ejected towards to the top plate,
which is connected to the negative of a variable power supply. The voltage is increased until the current
decreases to zero, and the voltage was recorded. The frequency was changed and the experiment
repeated. The following results were obtained:
Frequency
x 1014 (Hz)
5.3
6.9
7.75
8.25
9.9
11.9
Stopping voltage
(V)
0.45
1.3
1.5
1.9
2.7
3.33
DATA ANALYSIS QUESTIONS
[TOTAL: 23 marks]
GRAPH:
1.
Plot and label this experimental data for Sodium with frequency, ‘f’, in hertz, ‘Hz’ on the x-axis
and the stopping voltage, ‘V0’, in volts, ‘V’, on the y-axis: [4 marks]
 Labelled graph and axes [2 marks]
 Data points and line of best fit [2 marks]
2.
On the same axes sketch the graph (line of best fit) you would expect to get for Potassium,
given that it has a larger work function than Sodium: [2 marks]
DATA ANALYSIS:
3.
LINEAR ANALYSIS: Use your graph to determine values for Planck’s constant, ‘h’, the
threshold frequency, ‘f0’, and the work function, ‘W’, for the metal. Give the value of
Planck’s constant and in both joule seconds (Js) and in electronvolt seconds (eVs), similarly
give the value of the work function in both joule (J) and in electronvolts (eV).
Show all working out and explain your use of values from the graph [10 marks]

Plank’s constant in electronvolt seconds:
 h (eVs) [2 marks]

Plank’s constant in joule seconds:
 h (Js) [2 marks]

Threshold frequency in hertz:
 f0 (Hz) [2 marks]

Work function in electronvolts:
 W (eV) [2 marks]

Work function in joules:
 W (J) [2 marks]
CALCULATIONS:
4.
In the data above for the frequency of 7.75 x 1014 Hz, a voltage of 1.5 V stopped the most
energetic electron from crossing the gap. Use the data above to calculate the following:
Show all working out [4 marks]
 The magnitude of the electric force decelerating the electron (in newtons)
 Fe (N) [2 marks]
 The speed of the electron as it left the positive plate (in meters per second)
 ve (ms-1) [2 marks]
DISCUSSION:
5.
Describe how the Photoelectric Effect supports the particle model of light and does not support
the wave model of light: [3 marks]
GRAPH:
(use graph paper provided and be sure to label axes with appropriate units)
DATA ANALYSIS: (explain your use of values taken from the graph & show calculations)
LINEAR ANALYSIS:

h (eVs):

h (Js):

f0 (Hz):

W (eV):

W (J):
CALCULATIONS: (show formulae & calculations and use appropriate format & units)

ve (ms-1):

Fe (N):
DISCUSSION: