Question 11
Potential difference of 150 V is applied across an aluminum conductor of length 2.5 m. If the
density of free electrons in the conductor is 2 x 10
23
m
-3
, what would be the average drift
velocity of the electrons? (Conductivity of aluminum is 3.5 2 x 10
7
Ω
-1
m
-1
and charge on
electron = 1.6 x 10
-19
C)
A. 650.25 m/s
B. 450.65 m/s
C. 656.25 m/s
D. 414.55 m/s
E. 710.23 m/s
Correct Answer: C
Explanation:
Average drift velocity of an electron is given as
v
d
= σE / ne -------------- (1)
Electric field is given as
E = v/l --------------- (2)
Putting the values in equation 2 we get E = 150/2.5 Or E = 60 V/m
Putting the values in equation 1 we get v
d
= [(3.5 x 10
7
* 60) / (2 x 10
25
* 1.6 x 10
-19
)]
Or, v
d
= (2.1 x 10
9
) / 3.2 x 10
6
Or v
d
= 656.25 m.s
Therefore, C is the correct answer option.
Question 12
A beta particle of mass 9.1 x 10
-31
is moving perpendicular to a magnetic field in a region of
0.01 T with a speed of 10
4
m/s. What is the force experienced by the beta particle due to the
magnetic field? (Charge on electron = 1.6 x 10
-19
)
A. 3.2 x 10
-17
N
B. 1.6 x 10
-17
N
C. 4.8 x 10
-17
N
D. 2.4 x 10
-17
N
E. 10
-17
N
Correct Answer: B
Explanation:
Force experienced by the beta particle is given as
F = qvB sin θ ---------------- (1)
As the beta particle is moving perpendicularly to the magnetic field, θ = 90
o
. Charge onabeta particle
is equal to the charge onanelectron; Putting the values in equation 1 we get
F = 1.6 x 10
-19
x 10
4
x 0.01 x sin 90
o
Or, F = 1.6 x 10
-17
* 1 N
Or, F = 1.6 x 10
-17
Hence, B is the correct answer option.
