Page 33 - Q & A STPM 2022 Physics

Physics Semester 2 STPM Chapter 14 Electric Current
(iii) Current
density

Penerbitan Pelangi Sdn Bhd. All Rights Reserved.
P Q
(c) The increase in potential difference would increase the drift velocity of the
charge carriers.
v = I v ∝ I
nAe
The concentration of charge carriers remains unchanged because the
number of free electrons in the wire is the same.

14.4 Electric Conductivity and Resistivity

Section A Multiple-choice Questions

Question 1
–7
2
A metal wire has length 15 m, cross-sectional area 6.0 × 10 m and resistance
5.0 Ω. What is the conductivity of the wire?
A 2.0 × 10 Ω m –1 C 5.0 × 10 Ω m –1
–1
–1
–7
6
–7
–1
6
B 3.0 × 10 Ω m –1 D 7.5 × 10 Ω m –1
–1
Semester
2 Answer: C –7
ρ = RA = (5)(6 × 10 )
l 15
= 2.0 × 10 Ω m
–7
σ = 1 = 1
ρ 2 × 10 –7
= 5.0 × 10 Ω m –1
6
–1
Question 2
A copper wire of length 2.0 m has resistance 20 Ω. The wire is stretched to an
extension of 0.001 m. If the volume of the wire remains unchanged, what is the
new resistance of the wire?
A 20.01 Ω C 20.03 Ω
B 20.02 Ω D 20.04 Ω

232

014 STPM Q&A Physics T2.indd 232 17/02/2022 10:12 AM