## Tuesday, 23 September 2014

### Electric Circuits Questions

Question 1
 Each of the resistors in the circuit below has a resistance R Ohms. What is their total resistance (in terms of R). Question 2
a)
Four identical resistors are connected to a  battery of emf 12V and zero internal resistance, as shown below. What voltage would a voltmeter read when connected across the following points?

 i) A and D ii) A and B iii) A and C iv) B and C
b)
A short circuit (a wire of very low resistance) is connected across points C and D, as shown below. What voltage would a voltmeter now read when connected across the following points?

 i) A and D ii) A and B iii) A and C iv) B and C
Question 3
 a) Calculate the total resistance of the four resistors in the circuit shown below. b) Calculate the total resistance of the same four resistors when a wire of very low resistance is connected across points X and Y.
Questions 4 to 11 are all about the circuit drawn below. The cell has zero internal resistance Question  Calculate the total resistance of the circuit.
Question  Calculate the current I.
Question  Calculate the voltage across the points A and B.
Question  Calculate the current I1.
Question  How much charge will pass through the cell in 20s?
Question How much energy will be converted to heat by the 6 resistor in 5 minutes?
Question Calculate the power dissipated in the 8 resistor.
Question Calculate the total amount of energy converted to heat by all the resistors in 10 minutes

Question 12
 Calculate the maximum current which can be supplied by each of the following batteries a) a car battery of emf = 13·2V and internal resistance r = 0·15 b) a battery of eight cells each of emf = 1·6V and internal resistance r = 0·4 Question 13
 Two resistors, R1 = 3 and R2 = 6 , are connected in parallel with each other. They are then connected to a battery of emf, =10V and internal resistance r = 3 . Calculate a) the current flowing through the battery b) the current flowing through the 6 resistor.
Question 14
 A battery of emf, = 6V is connected to two 5 resistors in parallel with each other. If the current flowing through the battery is 2 A, calculate the internal resistance of the battery.
Question 15
 Three 12 resistors are to be connected to a battery of = 24V and r = 2 . Draw circuit diagrams showing how the resistors should be connected in order that the current flowing through the battery is a) 4A b) 1·2A c) 0·63A d) 2·4A
Question 16
 This question is about rms currents and voltages. For the circuit shown above calculate a) the rms value of the current, I b) the maximum value of the current c) the mean power dissipated in R1 d) the rms value of the voltage across R2.
Question 17
 A resistor is to be made using wire of diameter 0.2mm. The wire is made of nichrome of resistivity 1.50×10-6 m. a) Calculate the length of wire needed to make a resistor of resistance 15.0 . b) If the diameter of the wire was measured using a Vernier calliper having a precision of ±0.02mm what is the uncertainty in the value of the resistance made using the wire (state your answer in the usual way: resistance = R ± R ). Ignore any other sources of uncertainty in this calculation. c) Calculate the power dissipated in the resistor when a current of 1.5A flows through it. d) The resistor is found to change temperature by 2.4°CW-1 of power dissipated. After the current (1.5A) has been flowing for a few minutes, the temperature of the resistor will have increased. Given that the temperature coefficient of resistance of nichrome is 4.0×10−4°C-1, show that the change in resistance of the resistor is unlikely to cause too many problems.
Question 18
A thermistor, Rt (temperature dependent resistor) is to be used in a potential divider circuit as part of a thermostat. The heater is switched on (by circuits not shown) when the voltage across Rt is 1.25V. The graph shows the variation with temperature of the resistance of Rt.
Find the approximate temperature at which the heater will switch on
a)
with R = 9k b)
with R = 18k   