ABSTRACT
What is its frequency? (4) 2. For the periodic waveform shown in Figure RT15.1
determine: (a) the frequency, (b) the average value over half a cycle (use 8 intervals for a half cycle), (c) the r.m.s. value, (d) the form factor, (e) the peak factor. (12)
3. A sinusoidal voltage has a mean value of 3.0 V. Determine its maximum and r.m.s. values. (4)
4. An e.m.f. of 2.5 kV is induced in a coil when a current of 2 A collapses to zero in 5 ms. Calculate the inductance of the coil. (4)
5. A flux of 15 mWb links with a 2000-turn coil when a current of 2 A passes through the coil. Calculate (a) the inductance of the coil, (b) the energy stored in the magnetic field, (c) the average e.m.f. induced if the current falls to zero in 300 ms. (6)
6. A sinusoidal voltage trace displayed on an oscilloscope is shown in Figure RT15.2; the ‘time/cm’ switch is on 50 ms/cm and the ‘volts/cm’ switch is on 2 V/cm. Determine for the waveform (a) the frequency, (b) the peak-to-peak voltage, (c) the amplitude, (d) the r.m.s. value. (8)
7. An ammeter has a full scale defection. of 200 mA and a resistance of 40 . The ammeter is used to measure the current in a load of resistance 400 when the supply voltage is 20 V. Calculate (a) the ammeter reading expected (neglecting its resistance), (b) the actual current in the circuit, (c) the power dissipated in the ammeter, (d) the power dissipated in the load. (8)
8. In a Wheatstone bridge PQRS, a galvanometer is connected between P and R, and a battery between Q and S. A resistor of unknown value is connected between P and Q. When the bridge is balanced, the resistance between Q and R is 150 , that between R and S is 25 , and that between S and P is 500 . Calculate the value of the unknown resistance. (4)
For lecturers/instructors/teachers, fully worked solutions to each of the problems in Revision Test 15, together with a full marking scheme, are available at the website:
