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Questions and Answers
A current is defined as the flow of charge and is measured in coulombs.
A current is defined as the flow of charge and is measured in coulombs.
False
Conventional current flows in the same direction as negatively charged electrons.
Conventional current flows in the same direction as negatively charged electrons.
False
The equation for electric current is given by I = Q/t.
The equation for electric current is given by I = Q/t.
True
If 30 C of charge passes in 5 seconds, the current is 6 A.
If 30 C of charge passes in 5 seconds, the current is 6 A.
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The SI unit for current is the joule.
The SI unit for current is the joule.
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A charge of 8 C flowing for 2 seconds results in a current of 4 A.
A charge of 8 C flowing for 2 seconds results in a current of 4 A.
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When 10 C of charge passes through a point in 2 s, the current is 5 A.
When 10 C of charge passes through a point in 2 s, the current is 5 A.
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A current of 2 A flowing for 3 minutes results in a charge of 360 C.
A current of 2 A flowing for 3 minutes results in a charge of 360 C.
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The unit of resistance is measured in volts.
The unit of resistance is measured in volts.
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A resistor allows a current of 0.02 A to flow through it when there is a potential difference of 10.0 V, resulting in a resistance of 500 Ω.
A resistor allows a current of 0.02 A to flow through it when there is a potential difference of 10.0 V, resulting in a resistance of 500 Ω.
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A resistor has a resistance of one ohm if a current of two amperes flows through it when the potential difference across it is one volt.
A resistor has a resistance of one ohm if a current of two amperes flows through it when the potential difference across it is one volt.
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Electrical resistance opposes the flow of electric current.
Electrical resistance opposes the flow of electric current.
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When a wire is connected to a 9 V battery and a current of 0.020 A flows, the resistance of the wire is 450 Ω.
When a wire is connected to a 9 V battery and a current of 0.020 A flows, the resistance of the wire is 450 Ω.
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The potential difference across a moving-coil galvanometer with a resistance of 40 Ω and a current of 2 mA is 0.08 V.
The potential difference across a moving-coil galvanometer with a resistance of 40 Ω and a current of 2 mA is 0.08 V.
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Resistance is calculated using the formula resistance = current/potential difference.
Resistance is calculated using the formula resistance = current/potential difference.
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The current through a 12 Ω resistor with a potential difference of 6 V across it is 0.5 A.
The current through a 12 Ω resistor with a potential difference of 6 V across it is 0.5 A.
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Ohm's law states that the current in a conductor is proportional to the potential difference across it, provided that the temperature remains constant.
Ohm's law states that the current in a conductor is proportional to the potential difference across it, provided that the temperature remains constant.
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The effective resistance of three resistors connected in series is greater than the resistance of any of the individual resistors.
The effective resistance of three resistors connected in series is greater than the resistance of any of the individual resistors.
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When three identical resistors are connected in parallel, their combined resistance is less than that of each individual resistor.
When three identical resistors are connected in parallel, their combined resistance is less than that of each individual resistor.
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The current in a filament lamp increases as the temperature of the filament rises.
The current in a filament lamp increases as the temperature of the filament rises.
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Ohm's law can be applied at any point in the current-voltage graph of a resistor.
Ohm's law can be applied at any point in the current-voltage graph of a resistor.
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The combined resistance of three resistors connected in series is equal to the average of their individual resistances.
The combined resistance of three resistors connected in series is equal to the average of their individual resistances.
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If the voltage across a fixed resistance is doubled, the current will also double.
If the voltage across a fixed resistance is doubled, the current will also double.
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Increasing the thickness of a wire will decrease its resistance.
Increasing the thickness of a wire will decrease its resistance.
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A 20 Ω resistor needs a voltage of 20 V to make a current of 1 A flow.
A 20 Ω resistor needs a voltage of 20 V to make a current of 1 A flow.
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When a 14.5 V potential difference is applied across a 1000 Ω resistor, a current of 0.0145 A flows.
When a 14.5 V potential difference is applied across a 1000 Ω resistor, a current of 0.0145 A flows.
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A higher temperature always causes the resistance of all types of resistors to decrease.
A higher temperature always causes the resistance of all types of resistors to decrease.
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Ohm’s Law states that for a constant voltage, the current will decrease as the resistance increases.
Ohm’s Law states that for a constant voltage, the current will decrease as the resistance increases.
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The gradient of the voltage versus current graph represents the capacitance of the load.
The gradient of the voltage versus current graph represents the capacitance of the load.
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A rheostat is used to maintain a constant current in a circuit.
A rheostat is used to maintain a constant current in a circuit.
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The procedure for measuring resistance requires recording both the ammeter and voltmeter readings at multiple current values.
The procedure for measuring resistance requires recording both the ammeter and voltmeter readings at multiple current values.
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For a conductor to obey Ohm's Law, its resistance must be variable depending on the voltage applied.
For a conductor to obey Ohm's Law, its resistance must be variable depending on the voltage applied.
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A charge of 35 C requires 805 J of energy to move from a potential of 60 V to 83 V.
A charge of 35 C requires 805 J of energy to move from a potential of 60 V to 83 V.
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When 2 C of charge flows through a component and 20 J of work is done, the potential difference across the component is 5 V.
When 2 C of charge flows through a component and 20 J of work is done, the potential difference across the component is 5 V.
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It takes 180 J of work to move a charge of 30 C through a potential difference of 6 V.
It takes 180 J of work to move a charge of 30 C through a potential difference of 6 V.
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To toast a couple of slices of bread, a toaster uses 30,000 joules of energy from a 110 V outlet, resulting in a charge flow of approximately 272.73 C.
To toast a couple of slices of bread, a toaster uses 30,000 joules of energy from a 110 V outlet, resulting in a charge flow of approximately 272.73 C.
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In an electric current flowing through a metal wire, atoms are responsible for the flow.
In an electric current flowing through a metal wire, atoms are responsible for the flow.
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If the current in an electric heater is 10 A and it is switched on for five minutes, the total charge flowing through the heater is 3000 C.
If the current in an electric heater is 10 A and it is switched on for five minutes, the total charge flowing through the heater is 3000 C.
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The charge on an electron is positive and it flows from the positive terminal to the negative terminal of a battery.
The charge on an electron is positive and it flows from the positive terminal to the negative terminal of a battery.
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When connected in a circuit, identical resistors will have equal readings on all ammeters, assuming they share the same current.
When connected in a circuit, identical resistors will have equal readings on all ammeters, assuming they share the same current.
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Covering a wire in an insulating sleeve will reduce its resistance.
Covering a wire in an insulating sleeve will reduce its resistance.
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Increasing the cross-sectional area of a wire will decrease its resistance.
Increasing the cross-sectional area of a wire will decrease its resistance.
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A shorter and thicker wire will have a greater resistance than a longer and thinner wire.
A shorter and thicker wire will have a greater resistance than a longer and thinner wire.
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When the temperature of a wire decreases, its resistance will also decrease.
When the temperature of a wire decreases, its resistance will also decrease.
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A wire with a resistance of 8 Ω that is halved in length and doubled in cross-sectional area will also have a resistance of 4 Ω.
A wire with a resistance of 8 Ω that is halved in length and doubled in cross-sectional area will also have a resistance of 4 Ω.
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Study Notes
Current Electricity
- Current is the flow of charge, measured in amperes (A).
- Current is the rate of flow of charge (Q) over time (t).
- Charge = current × time
- The SI unit for current is coulomb per second (C/s) or Ampere (A).
- Electron flow is from negative to positive, but conventional current flows from positive to negative.
- In conductors, current is due to the motion of negatively charged electrons.
Electric Current
- Current is the rate of flow of charge.
- Electric charges can be positive or negative.
- Conventional current direction is taken as the direction of positive charge flow.
Calculating Current
- Suppose a charge Q flows past a point in a wire in time t.
- The electric current I in the wire is given by:
- I = Q/t
Problem Solving (Examples)
- Calculation of average current given charge and time.
- Calculation of current given charge and time.
- Calculation of charge given current and time.
Ammeter
- An ammeter measures current.
- Connects in series with the component.
- Has different ranges for different current values.
Electromotive Force (e.m.f.)
- e.m.f. is the energy dissipated per unit charge when a charge passes through the entire circuit.
- Measured in volts (V).
- e.m.f. = work done/charge
Cells in Series and Parallel
- In series, cells add up the e.m.f.s.
- In parallel, cells maintain the same voltage, increasing the total current capability.
Potential Difference (p.d.)
- p.d. is measured in volts (V).
- p.d. across a component is the work done per unit charge passed through it.
- p.d. = work done/charge or V = W/Q
Voltmeter
- A voltmeter measures the potential difference between two points in a circuit.
- Connects in parallel with the component.
- Has different ranges for different p.d. values.
Problems
- A collection of calculations to solve, and concepts related to how to solve them involving p.d. and current as examples
Resistance
- Resistance is the opposition to the flow of current (measured in ohms, Ω).
- The unit of resistance is the ohm (Ω). Resistor has a resistance of one ohm if a current of one ampere flows through it when the p.d. across it is one volt.
- Resistance = p.d/current (or voltage/current).
- Different materials and shapes can have a variety of resistances.
- The formula R = pl/A describes the proportional relationship between resistance, length, resistivity and cross-sectional area.
- Resistance and temperature are proportionally linked for some materials, while others change inversely.
- Resistors in series add to produce a higher combined resistance.
- Resistors in parallel add reciprocally to produce a lower combined resistance.
- Calculating resistance in different circuit arrangements.
Resistor
- A component that offers a known resistance.
- Used to control the current in a circuit.
- Has fixed or variable resistance.
Ohm's Law
- Current is proportional to potential difference (for components with constant resistance).
- The relationship between current, voltage and resistance are discussed.
- Current and voltage are directly proportional, with resistance as the constant of proportionality.
LDRs (Light Dependent Resistors)
- Resistance changes in response to light intensity.
- High resistance in darkness, low resistance in bright light.
- Uses in circuits and applications
Problem Solving (Examples)
- Sample problems relating to resistance, circuit analysis and Ohm’s Law concepts.
- Applications of calculations involving resistance, Ohm’s Law and potential difference.
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Description
Test your understanding of electric current and resistance with this quiz. Topics covered include the flow of charge, equations for current, resistance calculations, and the relationship between current and voltage. Ideal for students studying electricity concepts.
