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NCEA Electricity level 3 Exam Questions
And Answers 100% Guaranteed Pass.
Internal Resistance - Answer✔The internal resistance of a source is the loss of potential
difference per unit current in the source when current passes through a source. It is the resistance
encountered by a current as it passes through a battery. Gradient of current vs voltage graph. The
internal resistance will increase as the products of the reaction in the cells build up.
EMF - Answer✔The potential difference across the terminals of a voltage source when no
current is flowing from it is called the EMF. If a circuit is connected so that current flows from
the source, the voltage across the terminals will be less than the EMF
Kirchhoff's current law - Answer✔At any junction in a circuit, the sum of currents entering the
junction is equal to the sum of currents leaving it
Kirchhoff's voltage law - Answer✔Around any close loop in a circuit, the sum of the differences
in potential is zero
Capacitor - Answer✔A device that stores charge. A capacitor is a component which can store
electric charge and release it some time later.
Charging a Capacitor - Answer✔At the instant when the switch is closed, electrons will leave the
negative terminal and flow on to plate A, while an equal number of electrons will flow off plate
B on to the positive terminal. This flow of electrons will continue until the voltage across the
capacitor place equals the battery voltage. When this happens, the capacitor is fully charge.
- The capacitor voltage rises exponentially from zero to its maximum value
- The charging process stops when the capacitor voltage equals the batter voltage and so the
maximum capacitor voltage is the battery voltage
- The current falls exponentially from tits maximum value to zero
Fully Charged Capacitor - Answer✔- The flow of electrons stop
- Both plates have an equal and opposite amount of charge
- The potential difference across the places, V equals the supply voltage
- An electric field exists between the plates (strength of electric field = V/D)
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- The total charge stored has not changed. Because there is no change in the total charge stored,
there will be no movement of change and because current is the flow of charge, there is no
current.
Capacitance - Answer✔The capacitance of a capacitor is the amount of charge it can store when
connected across a potential difference of 1 volt.
Factors which determine capacitance - Answer✔- The area of the parallel plates
- The distance separating the plates
- The properties of the dielectric material between the plates. When an insulating material is
placed between the plates, the capacitance increases. This is called the dielectric effect. The
dielectric allows more charge to be stored.
Networks of capacitors - Answer✔In parallel
- The voltage across each capacitor is the same, therefore the total charged stored is the sum of
the charge in each capacitor
In series
- The charge on each capacitor is the same. The voltage of the capacitor add up to the supply
voltage, and the combined capacitance is given by the formula 1/Ct = 1/C1+ 1/C2
Energy Stored in a Capacitor - Answer✔When a capacitor is charged, it gains energy from the
voltage source. This energy is stored as electrical potential energy , When the capacitor is
discharged, the energy is dissipated in the resistance of the circuit as heat, light and etc, The
energy is the area under the voltage vs charge graph.
Discharging a capacitor - Answer✔The process of allowing the stored negative charge on one of
a capacitors plate to neutralise the positive charge on the other plate
- When the capacitor is discharged, the voltage across it becomes zero as the voltage falls
exponentially from its maximum value to zero, maximum value is the battery voltage.
- The current falls exponentially from tits maximum value to zero
Introduction of a resistor when the capacitor is fully charged - Answer✔Because there is no
current in the circuit, the voltage across the resistor is zero, and so by Kirchhoff's law, the battery
voltage must equal the capacitor voltage. Therefore the introduction of the resistor has had no
effect on the voltage (Vc).
Energy Stored in a Capacitor 2 - Answer✔When the capacitor is charging, the pull on the
electrons towards the positive battery will be working against the pull back on the electrons from
the positive plate. Equally, the push on the electrons by the negative terminal will have to work
against the push back from the negative plate. This work results in energy being store in the
capacitor
Energy Stored in a Capacitor 3 - Answer✔As soon as charge starts to build up on the plates, a
voltage across the plates is established. This voltage acts against the supply voltage, and so work
has to be done to make the charging process continue, therefore the energy stroed increases
2|Page
NCEA Electricity level 3 Exam Questions
And Answers 100% Guaranteed Pass.
Internal Resistance - Answer✔The internal resistance of a source is the loss of potential
difference per unit current in the source when current passes through a source. It is the resistance
encountered by a current as it passes through a battery. Gradient of current vs voltage graph. The
internal resistance will increase as the products of the reaction in the cells build up.
EMF - Answer✔The potential difference across the terminals of a voltage source when no
current is flowing from it is called the EMF. If a circuit is connected so that current flows from
the source, the voltage across the terminals will be less than the EMF
Kirchhoff's current law - Answer✔At any junction in a circuit, the sum of currents entering the
junction is equal to the sum of currents leaving it
Kirchhoff's voltage law - Answer✔Around any close loop in a circuit, the sum of the differences
in potential is zero
Capacitor - Answer✔A device that stores charge. A capacitor is a component which can store
electric charge and release it some time later.
Charging a Capacitor - Answer✔At the instant when the switch is closed, electrons will leave the
negative terminal and flow on to plate A, while an equal number of electrons will flow off plate
B on to the positive terminal. This flow of electrons will continue until the voltage across the
capacitor place equals the battery voltage. When this happens, the capacitor is fully charge.
- The capacitor voltage rises exponentially from zero to its maximum value
- The charging process stops when the capacitor voltage equals the batter voltage and so the
maximum capacitor voltage is the battery voltage
- The current falls exponentially from tits maximum value to zero
Fully Charged Capacitor - Answer✔- The flow of electrons stop
- Both plates have an equal and opposite amount of charge
- The potential difference across the places, V equals the supply voltage
- An electric field exists between the plates (strength of electric field = V/D)
1|Page
, ©THEBRIGHT 2024/2025 ALL RIGHTS RESERVED.
- The total charge stored has not changed. Because there is no change in the total charge stored,
there will be no movement of change and because current is the flow of charge, there is no
current.
Capacitance - Answer✔The capacitance of a capacitor is the amount of charge it can store when
connected across a potential difference of 1 volt.
Factors which determine capacitance - Answer✔- The area of the parallel plates
- The distance separating the plates
- The properties of the dielectric material between the plates. When an insulating material is
placed between the plates, the capacitance increases. This is called the dielectric effect. The
dielectric allows more charge to be stored.
Networks of capacitors - Answer✔In parallel
- The voltage across each capacitor is the same, therefore the total charged stored is the sum of
the charge in each capacitor
In series
- The charge on each capacitor is the same. The voltage of the capacitor add up to the supply
voltage, and the combined capacitance is given by the formula 1/Ct = 1/C1+ 1/C2
Energy Stored in a Capacitor - Answer✔When a capacitor is charged, it gains energy from the
voltage source. This energy is stored as electrical potential energy , When the capacitor is
discharged, the energy is dissipated in the resistance of the circuit as heat, light and etc, The
energy is the area under the voltage vs charge graph.
Discharging a capacitor - Answer✔The process of allowing the stored negative charge on one of
a capacitors plate to neutralise the positive charge on the other plate
- When the capacitor is discharged, the voltage across it becomes zero as the voltage falls
exponentially from its maximum value to zero, maximum value is the battery voltage.
- The current falls exponentially from tits maximum value to zero
Introduction of a resistor when the capacitor is fully charged - Answer✔Because there is no
current in the circuit, the voltage across the resistor is zero, and so by Kirchhoff's law, the battery
voltage must equal the capacitor voltage. Therefore the introduction of the resistor has had no
effect on the voltage (Vc).
Energy Stored in a Capacitor 2 - Answer✔When the capacitor is charging, the pull on the
electrons towards the positive battery will be working against the pull back on the electrons from
the positive plate. Equally, the push on the electrons by the negative terminal will have to work
against the push back from the negative plate. This work results in energy being store in the
capacitor
Energy Stored in a Capacitor 3 - Answer✔As soon as charge starts to build up on the plates, a
voltage across the plates is established. This voltage acts against the supply voltage, and so work
has to be done to make the charging process continue, therefore the energy stroed increases
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