Page 24 - Q & A STPM 2022 Physics

Physics Semester 2 STPM Chapter 14 Electric Current
Question 3

A conductor of length 2.0 m and cross-sectional area 5.0 × 10 m carries
2
–6
a current of 6.0 A. If the drift velocity of the conduction electrons is
1.5 × 10 m s , what is the number of electrons in the conductor?
–4
–1
Penerbitan Pelangi Sdn Bhd. All Rights Reserved.
A 2.5 × 10 C 4.2 × 10 23
23
B 2.9 × 10 23 D 5.0 × 10 23
Answer: D
I = nAve
= N Ave = Nve
Al l
N = Il
ve
= 6(2)
(1.5 × 10 )(1.6 × 10 )
–4
–19
= 5.0 × 10
23

Question 4
A tungsten wire of length 1.00 m and cross-sectional area 2.01 × 10 m carries
2
–6
a current of 5.00 A.
If the number of free electrons per unit volume is 4.3 × 10 , what is the time Semester
28
taken by an electron to travel from one end of the wire to the other end?
A 1.81 × 10 s C 4.51 × 10 s
3
3
B 2.77 × 10 s D 7.25 × 10 s 2
3
3

Answer: B
I = nAve
v = I
nAe
= 5
(2.01 × 10 )(4.3 × 10 ) (1.6 × 10 )
28
–19
–6
= 3.616 × 10 m s –1
–4
t = l
v
= 1
3.616 × 10 –4
= 2.77 × 10 s
3

223

014 STPM Q&A Physics T2.indd 223 17/02/2022 10:12 AM