23.1 Induced Emf and Magnetic Flux
To produce current with a coil and bar magnet you can:
- move the coil but not the magnet.
- move the magnet but not the coil.
- move either the coil or the magnet.
- It is not possible to produce current.
Calculate the magnetic flux for a coil of area 0.2 m2 placed at an angle of θ=60º (as shown in the figure above) to a magnetic field of strength 1.5×10-3 T. At what angle will the flux be at its maximum?
23.5 Electric Generators
The emf induced in a coil that is rotating in a magnetic field will be at a maximum when
- the magnetic flux is at a maximum.
- the magnetic flux is at a minimum.
- the change in magnetic flux is at a maximum.
- the change in magnetic flux is at a minimum.
A coil with circular cross section and 20 turns is rotating at a rate of 400 rpm between the poles of a magnet. If the magnetic field strength is 0.6 T and peak voltage is 0.2 V, what is the radius of the coil? If the emf of the coil is zero at t = 0 s, when will it reach its peak emf?
Which of the following statements is true for a step-down transformer? Select two answers.
- Primary voltage is higher than secondary voltage.
- Primary voltage is lower than secondary voltage.
- Primary current is higher than secondary current.
- Primary current is lower than secondary current.
An ideal step-up transformer with turn ratio 1:30 is supplied with an input power of 120 W. If the output voltage is 210 V, calculate the output power and input current.
23.8 Electrical Safety: Systems and Devices
Which of the following statements is true for an isolation transformer?
- It has more primary turns than secondary turns.
- It has fewer primary turns than secondary turns.
- It has an equal number of primary and secondary turns.
- It can have more, fewer, or an equal number of primary and secondary turns.
Explain the working of a ground fault interrupter (GFI).