+ A V switch variable resistor lamp The diagram shows a student investigating the current-voltage characteristic of a filament lamp. The student changes the...
Question 1 Report
The diagram shows a student investigating the current-voltage characteristic of a filament lamp. The student changes the setting of the variable resistor and records ammeter and voltmeter readings. At larger currents the metal filament gets hotter and emits more light. The student draws a graph of current against potential difference and finds that it is curved rather than a straight line. The apparatus includes a switch so that the lamp can be switched off between readings and does not overheat.
(a) Name the component used to change the current gradually. [1]
(b) Describe the shape of the current-potential difference graph for the lamp. [1]
(c) Explain why the resistance of the filament increases as current increases. [2]
Fig. 1 shows part of an audio amplifier used at a school concert. A microphone produces a small changing potential difference. The transistor circuit uses this changing signal to control a much larger current from a battery through a loudspeaker. The loudspeaker cone vibrates and produces sound waves. The circuit has three terminals, labelled base, collector and emitter. A technician checks that the signal cable is connected to the base terminal before the concert begins.
(a) Name the component used to amplify the microphone signal. [1]
(b) Give the output device shown in Fig. 1. [1]
(c) Explain how the transistor enables a small microphone signal to produce a louder sound. [2]
Answer Details
Filament lamp
(a) The component used to change current gradually is a variable resistor. [1]
(b) The current-potential difference graph is curved, becoming less steep as potential difference increases. [1]
(c) A larger current makes the filament hotter. In hotter metal, increased vibrations and collisions impede charge flow, so the resistance increases. [2]
Audio amplifier
(a) The amplifying component is a transistor. [1]
(b) The output device is a loudspeaker. [1]
(c) A small changing current or potential difference at the transistor’s base controls the transistor. This controls a much larger current from the battery through the loudspeaker, producing louder sound. [2]
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