(i) What are the charge carriers when electricity flows through gases? (6)
(ii) The graph plateaus in the region from A to B. Explain why this is so. (6)
(iii) With reference to the graph, justify the statement ‘conduction of electricity in gases does not obey Ohm’s law’. (4)
(iv) Give an application of a discharge tube. (3)
(d) A Wheatstone bridge was used to measure the resistance of a sample of nichrome wire. Fig 18.39 indicates the readings taken when the Wheatstone bridge was balanced.
(i) Calculate the resistance of the nichrome wire. (9)
(ii) What are the three factors that the resistance of the nichrome wire depend on? (9)
(iii) Name another device, apart from a Wheatstone bridge, that can be used to measure resistance. Give one advantage and one disadvantage of using this device instead of a Wheatstone bridge. (10)
3.1 9.7 5.4 A 0 V / V Fig 18.38 B
C
Nichrome wire
Fig 18.39
CHAPTER CHECKLIST FORMULAE:
■
■ ■ ■
■ ■ ■ ■
R V I
R R1 R2 P IV V IR
1 R 1
R1 R2
R1 R2
R1
1 R2
r RA l Rpd2
4l
R3 R4
l1 l2
Resistance Ohm’s law
Power
Resistors in series, derivation required at higher level only Resistors in parallel, derivation required at higher level only
