waec model questions vol1 2021 physics
Objective • Question 25
Question 25
WAEC_MODEL_QUESTIONS_VOL1
•
2021
A copper wire of length 2.0 m and cross‑sectional area $1.0\,\text{mm}^2$ has a resistivity of $1.68\times10^{-8}\,\Omega\,\text{m}$ at $20^{\circ}\text{C}$. Its temperature coefficient of resistance is $0.004\,\text{°C}^{-1}$. The wire is used as a heating element and is allowed to reach $120^{\circ}\text{C}$. Determine (i) the resistance of the wire at $120^{\circ}\text{C}$, (ii) the current that will cause it to dissipate $100\,\text{W}$ at that temperature, and (iii) the voltage across the wire at that current.
Answer Options
A.
R = 0.050 Ω; I = 44.7 A; V = 2.24 V
B.
R = 0.048 Ω; I = 45.6 A; V = 2.19 V
C.
R = 0.034 Ω; I = 54.5 A; V = 1.85 V
Correct Answer
D.
R = 0.047 Ω; I = 46.1 A; V = 2.17 V
Correct Answer
D
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