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SYSTEMS PREPARATION QUESTIONS 2008 - 2

V. Ryan © 2008

 

5. Explain why the gear system shown above (rack and pinion, question 4) is used where there are speed inclines.  
 
 
 
 
   
ANSWER

Trains cannot travel up steep inclines as their wheels have no grip. The rack and pinion allows the train to grip the track. The pinion is a special gear. Its teeth ‘mesh’ with the teeth on the rack, pulling the train up the incline.

   

6. Motion involves movement of some kind. Four types of movement are listed below. Label the diagrams that represent motion with the correct name.

ANSWER
 

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 carriages on a roller coaster. It is normally positioned before a riders platform. When a carriage is arriving the sensor detects a drop in the light level and a motor changes the signal and sounds a buzzer ensuring that the set of riders stand in the safe zone as it arrives.

A. Why has the circuits designer used a relay ?

 
 
 
 
   
POSSIBLE 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 - COMPONENT 'A':
 
 
FUNCTION:
 
 
   
ANSWER
   
8b. Name the component labelled ‘A’ and explain why its function.
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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