Download modern mini test Jan 2011

Unit 5 Test - Modern Physics
Problems (27 marks)
1. The rate of decay of a radioisotope is given in the following table. (2 marks)
Time (days)
0
3
6
9
12
Mass remaining (g)
320
160
80
40
20
a) What is the half-life of the radioisotope?
b) How much time is required (from the original 320 g sample) for the mass of the remaining radioisotope to
decrease to 5 g?
2. A particle has a de Broglie wavelength of 6.8  1014 m. Calculate the mass of the particle if it is travelling at
a speed of 1.4  106 m/s. (3 marks)
3. The energy level of an electron in the nth level of a hydrogen atom is given by the following equation.
En =
Find the frequency of the emitted photon when an electron falls from the fifth to the second level. (4 marks)
4. Write the equation for each reaction. (6 marks)
a) carbon-10 ( ) decayed by positron emission
b) gold-198 (
c) radium-223 (
) decayed by beta minus emission
) decayed by alpha emission
5. Blue light, with a frequency of 6.67  1014 Hz, is directed onto a metal surface with a work function of 2.60
eV.
a) Calculate the maximum kinetic energy, in joules, of the ejected electrons. (3 marks)
b) Calculate the stopping potential that will reduce the photocurrent to zero. Hint: Recall that an electron’s
charge is 1.60  1019 C and that V =
6. The binding energy of
. (3 marks)
is 127.5 MeV. Find its atomic mass. (6 marks)
Unit 5 Test - Modern Physics
Answer Section
PROBLEM
1. ANS:
a)
b) 3 days
c) 18 days
PTS: 1
2. ANS:
DIF: average
REF: MC
m=
=
= 6.9  1027 kg
PTS: 1
DIF: easy
3. ANS:
The energy of the emitted photon is
EE E
REF: K/U

Thus, the frequency of the photon is
f

PTS: 1
4. ANS:
DIF: difficult
REF: MC
a)
b)
c)
PTS: 1
DIF: average
REF: K/U
5. ANS:
a) E = hf  W
= (6.63  1034J s)(6.67  1014Hz)  (2.60 eV  1.60  1019 J/eV)
= 2.62  10
J
b) E = eV0
V0 =
=
= 0.16 V
PTS: 1
6. ANS:
Mass defect =
DIF: average
REF: MC
= 0.136 803 u
Calculate the nucleonic mass.
8 protons  1.007 276 u = 8.058 208 u
8 neutrons  1.008 665 u = 8.069 320 u
8.058 208 u + 8.069 320 u = 16.127 528 u
Nuclear mass = 16.127 528 u – 0.136 803 u = 15.990 725 u
Mass of 8 electrons = 8  0.000 549 u = 0.004 392 u
Total atomic mass = 15.990 725 + 0.004 392 u = 15.995 117 u
PTS: 1
DIF: average
REF: MC