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18 A strain gauge is a device that detects the way an b) The meters show the current in a resistor and the object changes shape when it is squashed, stretched voltage across it. or bent. The diagram shows how one is made. A thin current In m/ voltage In V piece of wire is set into a piece of flexible plastic. When the plastic is bent, the wire stretches. This causes the resistance of the wire to increase. 2.62 13.00 flexible plastic i) Copy the results table and add the readings on the two meters to the last column. [1] thin wire Current in MA 0.20 0.60 1.01 1.14 1.81 2.22 connecting lead Voltage in V. 1.0 3.0 15.0 7.0 9.0 11.0 a) Draw a diagram to show how the resistance of ii) Use the data in the table to draw a graph of the strain gauge can be measured using a battery, current against voltage. [5] ammeter and voltmeter. [2] ifi) Circle the anomalous point on the graph. [1] b) Before the gauge is stretched it is connected to a 6 V battery. A current of 30 mA flows through it. iv) How did you decide that this point was Calculate the gauge's resistance. [3] anomalous? [1] c) Explain why the resistance of the gauge increases v) Use your graph, or the table, to find the resistance when the wire is stretched. [1] of the resistor that the student used. [2] d) State what happens to the current in the circuit c) The student wants to investigate the effect of when the wire is stretched. [1] changing light intensity on a circuit. She sets up equipment outside in a garden for an experiment 19 A student is investigating the relationship between lasting 24 hours. She uses the circuit shown in voltage and current. the diagram. a) State the equation linking voltage, current and resistance. [1] i) Give the name of the component labelled X. [1] ii) List the variables that the student should measure. [2] ifi) Explain why the student might need help to take all the readings for this investigation. [2]