Page 36 - Q & A STPM 2022 Physics

Physics Semester 2 STPM Chapter 14 Electric Current
Answer: Exam Tips
(a) R c = ρ c l = ρ c l Exam Tips
2
2
A c π(r 2 – r 1 ) Cross-sectional area of
(1.7 × 10 )(0.5) copper sheath:
–8
= 2 2
2
2
π(2 – 1.5 ) × 10 –6 A = π(r 2 – r 1 )
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= 1.546 × 10 Ω
–3
–7
(b) R i = ρ i l = (1 × 10 )(0.5)
–3 2
A i π(1.5 × 10 )
= 7.074 × 10 Ω
–3
(c) The sheath and the core are arranged in parallel.
1 = + 1
1
R R c R i
1 1
= +
1.546 × 10 –3 7.074 × 10 –3
\ R = 1.269 × 10 Ω
–3
(d) V = IR
0.012 = I(1.269 × 10 )
–3
I = 9.46 A
Question 6 Semester
A thin square slab is cut from a sheet of metal of uniform thickness t as shown
in the diagram.
2
L
Y t
L
x

t
Z
(a) If the resistivity of the metal is ρ, find the resistance of the metal slab when
a current flows in the direction of
(i) x (ii) y (iii) z
Explain whether the resistance depends on the value of L and t in each case.
(b) Another square slab of sides 2L is cut from the same metal. If the current
flows in the direction of y, find the ratio of the resistance of the second slab
to the resistance of the first slab.

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