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Weekend Quiz. Back to Basics.

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Q.1. There are two resistors in series in a circuit, of 18 Ohms and 22 Ohms resistance. The current through the 18 Ohm resistor is 6 Amps. Calculate the supply Voltage to the circuit.


Q.2 There are three resistors of resistance 20 Ohms, 10 Ohms and 8 Ohms connected in parallel to a 6 Volt D.C. supply. Calculate:


a, The total resistance.


b, The current taken from the supply.


Q.3. A coil of 30 Ohms reactance is connected to a 200 Volt A.C. supply circuit, in series with a of 50 Ohms resistance. A capacitor of 30 Ohms reactance is connected in series with the coil. Calculate,


a, The circuit impedance.


b, The current drawn from the supply.


c, The power used.


Q.4. An electric heater uses 5.4MJ in 45 minutes. What is the rating of the element?


a, 1kW.


b, 1.5kW.


c, 2kW,


d, 3kW.


Q.5 The input of an electric motor is 5.8kW. The output is 4.75kW. The efficiency is,


a, 1.05%


b, 10.5%


c, 82%


d, 122%


Z.


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  • 0
    Thanks all,

                         Ancient Mariners are good at physics and maths it seems. All correct.


    Ref. Q.3 (a)  The 30 Ohm reactance of the capacitor and the 30 Ohm reactance of the coil cancel out to zero effect. So, x = 30-30=0. Therefore Z=R.


    Q.4. Watts=Joules (energy) divided by time (seconds). One Watt=One Joule per Second.


    Q.5. Efficiency = OUTPUT divided by INPUT and is always less than 100 percent as all machines have losses.


    Z.




Reply
  • 0
    Thanks all,

                         Ancient Mariners are good at physics and maths it seems. All correct.


    Ref. Q.3 (a)  The 30 Ohm reactance of the capacitor and the 30 Ohm reactance of the coil cancel out to zero effect. So, x = 30-30=0. Therefore Z=R.


    Q.4. Watts=Joules (energy) divided by time (seconds). One Watt=One Joule per Second.


    Q.5. Efficiency = OUTPUT divided by INPUT and is always less than 100 percent as all machines have losses.


    Z.




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