1(a) hf
= f
hf = 4.60 x 10-19
f = 4.60 x 10-19 / 6.63 x 10-34
= 6.94 x 1014 Hz
(b) hf = f + (1/2) mv2. (6.63 x 10-34 x 7.30
x 1014) = 4.60 x 10-19 + (1/2) mv2
4.84 x 10-19
- 4.60 x 10-19 = (1/2) mv2
= 0.24 x 10-19 J
2
|
Metal
|
Work
Function
/
eV
|
Work
Function
/ J
|
Frequency
used
/ Hz
|
Maximum
KE of
ejected
electrons / J
|
|
Sodium
|
2.28
|
3.65 x 10-19
|
6 x
1014
|
0.35 x 10-19
|
|
Potassium
|
2.30
|
3.68
x 10-19
|
6 x 1014
|
0.32
x 10-19
|
|
Lithium
|
2.90
|
4.64 x 10-19
|
1.
x 1015
|
1.99 x 10-19
|
|
Aluminium
|
4.10
|
6.56 x 10-19
|
1.04 x 1015
|
0.35
x 10-19
|
|
Zinc
|
4.30
|
6.88 x 10-19
|
1.2 x 1015
|
1.12
x 10-19
|
|
Copper
|
4.60
|
7.36
x 10-19
|
1 x
1015
|
0
|
For copper 1 x 1015 Hz is below the threshold
frequency so no electrons are ejected.
3)
(a) 1.07
x 10-18 J
(b) hf
= f + eVs, so f = hf - eVs, so f = 1.07 x 10-18 –
(1.6 x 10-19 x 3) = 5.9 x 10-19
J
(c) eVs
= (1/2) mv2 so (1.60 x 10-19
x 3) = 0.5 x 9.11 x 10-31 x v2
so v2
=1.04 x 1012 and v = 1.02 x 106 m s-1
4 1.2 x 1015 Hz
5
(a) 1.6 x 10-18 J
(b) (1/2) mv2 = 1.0 x 10-18
J
(c) v2 = 1.1 x 1012 so
v = 1.1 x 106 m s-1
(d) (not
in spec) eVs = (1/2) mv2 so eVs = 1.00
x 10-18 and Vs = 0.63 V
