Physics 5054 · O Level · Resistance

Resistance — practice question

A student explores how the resistance of a light-dependent resistor (LDR) changes with light brightness. He uses a lamp to alter the brightness falling on the LDR. The LDR is fixed to a wooden block so that it stands a distance $l$ above the bench. The lamp is positioned directly above the LDR at a height $h$ above the bench, as shown in Fig. 1.1.
(a(i))[1]

Measure $l$ and $h$ on Fig. 1.1.

(a(ii))[1]

Calculate the distance $d$ from the lamp to the LDR.

(a(iii))[1]

The student uses a ruler to measure $h$. Suggest one difficulty the student may face when taking this measurement.

(b(i))[2]

Draw a circuit diagram for this apparatus in the space below.

(b(ii).1)[1]

Record the values of $V$ and $I$.

(b(ii).2)[2]

The resistance $R$ of the LDR for this lamp position is found using the equation $R = \frac{V}{I}$. Calculate $R$, giving your answer to 2 significant figures with unit.

(c(i))[4]

Use the readings obtained in (a)(ii) and (b)(ii) to complete the first row of Table 1.1. On the grid in Fig. 1.4, plot the graph of $I/\text{mA}$ on the $y$-axis against $d/\text{cm}$ on the $x$-axis. Begin both axes at $(0,0)$. Draw the smooth curve of best fit.

(c(ii))[1]

The voltage $V$ remains constant throughout. Suggest how the resistance $R$ of the LDR changes with $d$.

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