Q9. Fig shows a. d. c. relay circuit, when the supply is switched on the coil current rises to a final value of 16 mA with a time constant of 1.8 ms. The relay contact close when the current is 11.20mA.
(a) calculate EACH of the following:
(i) the coil resistance; (2)
(ii) the coil inductance; (2)
(iii) the time taken for the relay contact to close. (4)
(b) when the supply is switched off the coil current falls with a time constant of 2.5 ms, and the relay contact opens when the current is 2 mA.
(i) State the purpose of the diode. (2)
(ii) calculate the time taken to open the relay contact, assuming the diode has negligible forward resistance. (4)
(iii) state why a resistor connected in series with the diode will reduce the time taken to open the relay contact. (2)
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