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SYSTEMS PREPARATION 2007 - QUESTIONS - 2
 
V. Ryan 2007-2017
 
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6. Motion involves movement of some kind. Four types of movement are listed below. Label the diagrams that represent motion with the correct name.
 
 
 
 
7. The items listed below all involve movement. Label each diagram with the correct type of movement
 
 
ANSWER
 
 
8. The sensor circuit seen below is used to sense the movement of model trains. It is normally positioned before a model railway station. When a train is arriving the sensor detects a drop in the light level and a motor changes the signal and sounds a buzzer
 
 
8a. Why has the circuits designer used a relay ?
 
 
 
 
 
ANSWER
 
The relay separates the two circuits. The sensor operates using 9 volts whilst the secondary circuit operates using 24 volts. The relay separates the two sources of power as well as the two sets of components.
 
 
 
8b. Name the component labelled ‘A’ and explain why its function.
 
NAME:_______________________________
 
 
 
 
 
ANSWER
 
NAME: DIODE
 
FUNCTION: To protect the circuits components form back EMF. When current to a relay is removed the relay can emit current, sending it round the circuit in the opposite direction. This can damage sensitive components such as transistors. The diode prevents this happening.
 
8c. What happens to reading on the voltmeter when a train passes the sensor ?
 
 
 
 
 
ANSWER
 
When the train passes the sensor circuit the light level drops. This increases the resistance of the LDR. Current no longer flows through the LDR and consequently flows to the base of the transistor. The voltmeter will show an increase as a result.
 
 
 
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