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.

Type

Multiple choice Written

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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 $V/I$

Question 2

Paper 2Medium7 marks

A positive charge $q$ moves between the terminals of component P or component Q in the direction of conventional current. $W$ is the electrical work transferred to the component. For each component, the potential difference is constant during the measurements. Figure 1 shows measured values of $W$ for different values of $q$ Treat potential differences as magnitudes.

(a)

Explain why the gradient of a graph of $W$ against $q$ represents the potential difference across a component.

[2]

(b)

Determine the potential difference across component P using Figure 1.

[2]

(c)

A positive charge of $0.60\ \mathrm{C}$ passes through component Q. Determine the work transferred to Q. State which component transfers more energy per unit charge, and by what factor.

[3]

Question 3

Paper 2Medium9 marks

The circuits in Figure 1 are used to compare solid samples X and Y. The sources are ideal and the ammeters have negligible resistance. The samples have equal length and cross-sectional area and are each maintained at $20^\circ\mathrm{C}$

(a)

Identify which sample is an insulator.

[1]

(b)

Determine the resistance of each sample.

[3]

(c)

The voltage across X is then reduced to $1.5\ \mathrm{V}$ Its temperature remains at $20^\circ\mathrm{C}$ and its resistance is assumed unchanged. Calculate the electrical energy transferred to X in $40\ \mathrm{s}$ Show your working.

[3]

(d)

Explain, in terms of the mobility of charge carriers, why the readings in Figure 1 are consistent with X being a conductor and Y an insulator.

[2]

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