Distinguish between resistance and resistivity. What is the effect on the resistance of a length of wire if the diameter of the wire is increased by a factor of three? In the circuit diagram shown, the a.c. supply has an rms voltage of 12 V. The variable resistor is set at 500 Ω. is meant by rms? What is meant by a.c.? Calculate the effective resistance of the circuit Calculate the current flowing in the 200 Ω resistor. The variable resistor is then removed. What effect will this have on the current flowing in the 50 Ω resistor? Explain your answer. Wheatstone bridge and metre bridge 2012 Question 9 [Higher Level] Define resistance. Two resistors of resistance R1 and R2 are connected in series. Derive an expression for the effective resistance of the two resistors in terms of R1 and R2. 4 Ω resistors are connected in parallel. Draw a circuit diagram to show how another 4 Ω resistor could be arranged with these two resistors to give an effective resistance of 6 Ω. A fuse is a resistor used as a safety device in a circuit. How does a fuse operate? A Wheatstone bridge circuit is used to measure the resistance of an unknown resistor R. The bridge ABCD is balanced when X = 2.2 kΩ, Y = 1.0 kΩ and Z = 440 Ω. What test would you use to determine that the bridge is balanced? What is the resistance of the unknown resistor R? When the unknown resistor R is covered by a piece of black paper, the bridge goes out of balance. What type of resistor is it? Give a use for this type of resistor. 2014 Question 10 {second half} The resistance of the conductor in a strain gauge increases when a force is applied to it. Strain gauges can act as the resistors in a Wheatstone bridge, and any change in their resistance can then be detected. How would an observer know that a Wheatstone bridge is balanced? The Wheatstone bridge in the diagram is balanced.
What is the resistance of the unknown resistor? an expression for the resistance of a wire in terms of its resistivity, length and diameter. The radius of a wire is doubled. What is the effect of this on the resistance of the wire? 2007 Question 9 [Higher Level] Define resistance. Define resistivity. A metre bridge was used to measure the resistance of a sample of nichrome wire. The diagram indicates the readings taken when the metre bridge was balanced. The nichrome wire has a length of 220 mm and a radius of 0.11 mm. Calculate the resistance of the nichrome wire the resistivity of nichrome. Sketch a graph to show the relationship between the temperature and the resistance of the nichrome wire as its temperature is increased. What happens to the resistance of the wire as its temperature falls below 0oC? What happens to the resistance of the wire as its length is increased? What happens to the resistance of the wire if its diameter is increased? Name another device, apart from a metre bridge, that can be used to measure resistance. Give one advantage and one disadvantage of using this device instead of a metre bridge. Solutions to ordinary Level maths questions 2013 Question 9 (b) [Ordinary Level] State Ohm’s law. The current through a conductor is directly proportional to the voltage Calculate the total resistance of the circuit. 6 + 12 = 18 Ω the current in the circuit. I = = 0.166 A Calculate the potential difference across the 6 Ω resistor. V = IR = (0.166)(6) = 1 V Name an instrument used to measure potential difference. voltmeter 2013 Question 12 (d) [Ordinary Level] State Ohm’s law. Ohm’s Law states that the current flowing through a conductor is directly proportional to the potential difference across it, assuming constant temperature.