IB Physics HL B.5 Current and circuits questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

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Question 1

Multiple choiceMedium1 mark

A metal wire is connected as shown. Its temperature is held constant for the first readings, then allowed to rise as the potential difference is increased. Which row describes the first readings and the resistance trend in the later readings?

	Behaviour of first readings	Resistance during later readings
A	Ohmic	Increases
B	Ohmic	Decreases
C	Non-ohmic	Increases
D	Non-ohmic	Decreases

Show answer and explanation

Answer: A. Resistance is $R=V/I$ For the fixed-temperature readings, $1.0/0.20=5.0\ \Omega$ and $2.0/0.40=5.0\ \Omega$ so current is proportional to potential difference and the wire is ohmic. For the later readings, $3.6/0.60=6.0\ \Omega$ and $5.6/0.80=7.0\ \Omega$ so resistance increases.

B: treats the falling gradient of the current-against-potential-difference graph, $I/V$ as resistance; its decrease corresponds to increasing $V/I$

C: uses the changing gradient in the later section to classify the fixed-temperature readings, which lie on a straight line through the origin.

D: combines those errors, applying the later section’s changing gradient to the first readings and reversing resistance with $I/V$

Remember: On an $I$ -against- $V$ graph, the gradient is $I/V$ whereas resistance is $V/I$

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