Transformer

What is the function of a transformer?

• To transfer magnetic fields

• To connect separate circuits together

• To change the voltage of an alternating current

How is a voltage produced on a transformer's secondary coil?

• The changing magnetic field in the core cuts across the secondary coil, inducing a voltage

• The current in the primary coil conducts through the iron core and into the secondary coil

• The secondary coil is attached to an external power supply

Which type of current makes a transformer work?

• ас

• dc

• either ac or dc

Why is a transformer core made from iron?

• Iron is very dense

• Iron is easily magnetised

• Iron is cheap

Which of these is the correct equation for calculating electrical power?

• Power (J) = current (A) × potential difference (V)

• Power (W) = current (A) × potential difference (V)

• Power (J) = current (A) ÷ potential difference (V)

Which of these equations correctly links potential differences and number of turns on the coils in transformers?

• $\frac{Vp}{Vs}=\frac{Ns}{Np}$

• $Vs\cdot Ns=Vp\cdot Np$

• $Vs\cdot Np=Vp\cdot Ns$

What kind of transformer converts 230,000 V into 11,500 V?

• Step-down

• Step-out

• Step-up

A transformer has 420 turns on its primary coil. How many turns on the secondary coil are needed for it to increase the voltage by a factor of three?

• 140

• 420

• 1260

A transformer converts 460 V into 230 V. The power output is 2.3 kW, how much current is drawn into the primary coil?

• 4.6 A

• 5.0 A

• 1.15 A

Why do National Grid overhead transmission cables use very high voltages?

• Higher voltages mean higher currents which wastes less energy

• Higher voltages mean lower currents which wastes more energy

• Higher voltages mean lower currents which wastes less energy