HALF QUESTION Typical of Question 12 in Leaving Cert. Exam Q5 Answer all of the following parts (a), (b), (c), (d) and (e). (a) What is a magnetic field?
The Earth has a magnetic field. Give one use of the Earth’s magnetic field. Describe an experiment to demonstrate the magnetic effect of an electric current. Draw a sketch of the magnetic field around a straight wire carrying a current.
(b) Define magnetic flux.
A rectangular coil, of sides 8 cm and 4 cm, lies perpendicular to a magnetic field of flux density 10.0 T. The coil consists of 1 000 turns of wire.
(i) What is the magnetic flux cutting the coil?
(ii) The coil completes five revolutions per second. Calculate the magnitude of the average emf induced in the coil while it is being rotated.
(c) The transformer is a device based on the principle of electromag- netic induction.Name two devices that use transformers. (6)
Name the parts of the transformer labelled A, B and C in Fig 20.38. (9)
The mains electricity supply (230 V) is connected to A, which has 1 000 turns. C has 200 turns.What is the reading on the voltmeter? (9)
How is the part labelled B designed to make the transformer more efficient? (4)
The efficiency of a transformer is 90 per cent.What does this mean? (d) What is self-induction?
A long straight wire is connected in series with an ammeter and an a.c. power supply and the current is noted.The wire is then wound around an iron nail many times.What effect, if any, does this have on (i) the resistance of the wire and (ii) the current flowing in the circuit? Explain.
What effect would removing the nail from the centre of the coil have on the current? Give an application of the principle demonstrated here.
(e) What is the difference between mutual induction and self-induction? Describe an experiment to demonstrate mutual induction. Describe an experiment to demonstrate self-induction.
