Page 37 - Q & A STPM 2022 Physics

Physics Semester 2 STPM Chapter 14 Electric Current
Answer:
Exam Tips
ρL ρ Exam Tips
(a) (i) R x = Lt = t
The resistance is independent of L Formula used:
ρl
but dependent on t. R = A
Penerbitan Pelangi Sdn Bhd. All Rights Reserved.
ρt
(ii) R y =
L 2
The resistance is dependent on L and t.
ρL ρ
(iii) R z = Lt = t
The resistance is dependent on t but independent of L.
ρt ρt
(b) R 1 = L 2 , R 2 = (2L) 2
ρt
= 4L 2
ρt L 2
R 2
\ = 2 ×
R 1 4L ρt
1
=
4

Section C Essay Question
Question 7

(a) What is meant by resistivity and conductivity of a substance? [2]
Semester
2 (b) Show that the conductivity of a substance σ = ne τ . [5]
2
m
(c) The conductivity of a copper wire decreases with increasing temperature
but the conductivity of a sample of pure silicon increases as temperature
rises. Explain the dependence of conductivity on temperature for copper
and silicon. [5]
(d) State the effects of temperature change on the resistivity of conductors,
semiconductors and superconductors. [3]

Answer
(a) Resistivity of material, ρ = RA , R = resistance of a wire of that material
l
A = cross-sectional area of the wire
l = length of the wire
1
Conductivity, σ = resistivity, ρ of materials

236

014 STPM Q&A Physics T2.indd 236 17/02/2022 10:12 AM