Electric Fields
(Unit Two summary pages 1, 2 and 3)
1. Draw the electric field patterns for:
a) a positive point charge
b) a negative point charge.
2.
In the above diagram the charge on Q is 5μC. If the potential difference between A and B is
12V, calculate:
a) the electrical potential energy gained.
b) the kinetic energy gained on reaching the positive plate.
3. An electron is accelerated from rest through a potential of 100V. Calculate:
a) the kinetic energy gained by the electron.
b) the final speed of the electron.
(All other necessary data can be found on the Summary Sheet)
Current, Power and Resistance
(Unit Two summary pages 4 and 5)
1. A toaster which is connected to the mains supply draws a current of 5A. Calculate the
resistance of the toaster’s heating element.
2. A 240Ω resistor is connected to a power output of 0.6W. How much current will flow
through the resistor?
3. A 4kΩ resistor is connected to a power output of 40W. What is the potential difference
across the resistor?
4. What is the total resistance when a 3Ω, 4Ω and a 12Ω resistor are connected in series?
5. What is the total resistance when the resistors in Q.4 are connected in parallel?
EMF
(Unit Two summary pages 6 and 7)
1. What is meant by the EMF of a cell?
2. What is the cause of “lost volts” in a power supply?
3. A voltmeter is placed across a cell and records an open circuit voltage of 4.0V.When a
current of 1.6A is flowing in the circuit the voltmeter reads 3.2V.
a) What is the value of the EMF of the cell?
b) What is the cell’s terminal potential difference?
c) Calculate the value of the cell’s internal resistance.
d) Calculate the value of R the load resistance in the circuit.
e) Calculate the cell’s terminal potential difference if the value of R is halved.
Wheatstone Bridge
(Unit Two summary page 8)
1. Draw a Wheatstone Bridge circuit and state the relationship between the four resistors
when the circuit is balanced?
2. For a balanced Wheatstone Bridge what does the voltmeter or galvanometer always read?
3. Sketch a graph (no numerical values needed) to show the relationship between out-ofbalance p.d. and change in resistance for a Wheatstone Bridge circuit.
4. In an initially balanced Wheatstone Bridge circuit, one resistor is altered by 2mΩ and the
out-of-balance p.d. is 8mV. If the same resistor is altered by 15mΩ, what will be the out-ofbalance p.d.?
5. The following resistors are available for your circuit in Q.1 - 500Ω, 1.5kΩ, 2kΩ and 6kΩ.
Re-draw your circuit diagram to show the following conditions:
a) A balanced Wheatstone Bridge.
b) The maximum possible p.d. reading on the voltmeter.
c) The minimum non-zero p.d. reading on the voltmeter.
Alternating Current and Voltage
(Unit Two summary pages 9, 10 and 11)
1. The time-base of a CRO is set to 2mscm-1. If four complete waves occupy 10cm, what is
the frequency of the waves?
2. State the peak value and the rms value for voltage in the UK.
3. The peak value of an alternating current in a 10Ω resistor is 3.0A. Calculate the power
developed in the resistor.
4. A 4Ω resistor is connected to a 24V peak supply. What is the rms current?
5. An ac supply is connected to a CRO and a 5cm vertical line appears on the screen.
a) Which CRO control needs to be turned on to view the trace correctly?
b) What is the rms voltage if the Y-gain is set at 2Vcm-1?
Capacitance
(Unit Two summary pages 12 and 13)
1. What is meant by the expression “ a capacitance of 5µF”?
2. A 230V dc supply, a 47µF capacitor, a switch and a resistor are connected in a series
circuit.
a) Draw this circuit – assume the switch is open and the capacitor is uncharged.
b) Sketch a graph of charge vs. potential difference for the circuit from when the switch is
closed until the capacitor is fully charged. (No numerical values needed)
c) What is the potential difference across the capacitor when it is fully charged?
d) Calculate the energy stored in the capacitor when it is fully charged?
Capacitance Graphs
(Unit Two summary pages 14 to 17)
1. Draw and clearly label the graphs which illustrate the following:
a) Current vs time during the charging of a capacitor.
b) Current vs time during the discharging of a capacitor.
c) Current vs frequency in a capacitive circuit.
d) Current vs frequency in a resistive circuit.
e) Voltage vs time during the charging of a capacitor.
f) Voltage vs time during the discharging of a capacitor.
2. A 200µF capacitor is charged until the voltage across its plates is 50V.
a) How much charge has been stored during the charging process?
b) The capacitor can be discharged in 2.5ms. What is the average current during discharge?
Operational Amplifiers One
(Unit Two summary pages 19 to 22)
1. Draw the symbol for an operational amplifier and clearly add the following labels:
inverting terminal; non-inverting terminal; output terminal; supply voltages
2. Draw an operational amplifier connected in the “inverting mode”.
3. For the operational amplifier in Q.2, what is the value of V0 when R1 = 4kΩ, Rf = 10MΩ
and V1 = 6mV? Explain why a voltmeter measures the value of V0 as 13V.
4. In the previous question, V1 was an ac voltage. In what three ways would V0 differ from
V1? (A diagram can be used to help your explanation)
Operational Amplifiers Two
(Unit Two summary pages 23 to 27)
1. Draw an operational amplifier connected in the “differential mode”.
2. For the operational amplifier in Q.1, what is the value of V0 when R1 = R2 = 10kΩ,
R3 = Rf = 40kΩ, V1 = 0.5V and V2 = 0.95V? Explain the significance of your answer for a
control circuit that uses a MOSFET.
3. Draw a Wheatstone Bridge/Differential Amplifier/NPN Transistor control circuit that will
operate a warning buzzer when a thermistor detects an increase in temperature.