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| SYSTEMS PREPARATION 2007 - QUESTIONS - 2 |
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| V. Ryan © 2007-2017 |
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| PDF FILE - CLICK HERE FOR PRINTABLE WORKSHEET |
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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. |
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| 7. The items listed below all involve movement. Label
each diagram with the correct type of movement |
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| ANSWER |
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| 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 |
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| 8a. Why has the circuits designer used a
relay ? |
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| ANSWER |
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| 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. |
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| 8b. Name the component labelled ‘A’ and
explain why its function. |
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| NAME:_______________________________ |
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| ANSWER |
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| NAME: DIODE |
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| 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. |
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| 8c. What happens to reading on the voltmeter
when a train passes the sensor ? |
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| ANSWER |
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| 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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