K.C.S.E Physics Q & A - MODEL 2011PP2QN07&8

K.C.S.E Physics Q & A - MODEL 2011PP2QN07&8

​Figure 5, shows a motor connected to a magnetic switch called a relay operated by an ordinary switch S1 Use the information in the figure to answer questions 7 and 8.

​Explain how the relay switches on the motor when S1 is closed. 
State with a reason the effect on the motor, the iron core is replaced with a steel core and switch S1 is put on and then off. 

ANSWERS

• ​7. When S is closed, current flows in solenoid magnetizing the iron core; this attracts the iron armature closing the contacts; this causes current to flow in the motor circuit:
• Motor keeps running continuously; 
• 8. Steel would remain permanently magnetized causing current in mortor circuit to remain when S is open.