**1. **Explain the principle of operation of the polyphase induction motor.

**2. **Show that a rotating magnetic field can be produced by the use of 3-phase currents of equal magnitude.

**3. **What is meant by slip in an induction motor? Develop an expression for the frequency of rotor currents in it.

**4. **Derive an expression for the torque of an induction motor and obtain the condition for maximum torque.

**5. **Show that in a 3-phase induction motor with negligible stator impedance maximum torque is developed R at slip s = R_{2/X2 }where R_{2} and X_{2} are rotor

resistance and standstill reactance respectively.

**6. **State the effects of increasing rotor resistance on starting current, starting torque, maximum torque and full-load slip of an induction motor.

**7. **Show that in an induction motor the rotor input: power developed: rotor copper losses: 1:(1 – s) : s, where s is the fractional slip.

**8. **Draw equivalent circuit of a 3-phase induction motor.

**9. **Describe and explain how to perform a locked rotor test. What data can be obtained by the test?

**10. **What are no-load and blocked rotor tests? What sort of losses can be measured by these tests?

**11. **How would you determine circle diagram of a 3-phaseinduction motor experimentally?

**12. **Describe the constructional details of a 3·phase squirrel-cage and phase wound induction motors. Also discuss the applications of various types of starters used for starting these motors.

**13. **Why at all starters are necessary for starting the induction motors? What are the various types of starters used for squirrel-cage motors? Discuss them.

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