Define electric charge .

Electric charge is a property of matter that can be either positive or negative .

Electric charge is measured in units called ______ .

Electric charge is measured in units called coulombs (C).

What type of force acts between two objects that carry the same type of charge?

A repulsive force — the objects push apart.

What type of force acts between two objects that carry opposite types of charge?

An attractive force — the objects pull towards each other.

True or False? Two objects that are both negatively charged will attract each other when brought close together.

False. Objects with the same charge (both negative, or both positive) repel ; only objects with opposite charges attract.

Define electrostatic repulsion .

Electrostatic repulsion is the repulsive force that acts between two objects carrying the same type of charge .

Rubbing an insulating rod with a cloth transfers ______ from its surface, leaving the rod with an overall positive charge.

Rubbing an insulating rod with a cloth transfers electrons from its surface, leaving the rod with an overall positive charge.

In the cradle method for demonstrating electrostatic charge, how is the test material suspended?

By a length of thread (string) hung from a clamp stand , so that it can rotate freely.

In the cradle method, what result shows that two charged rods carry the same type of charge?

The suspended rod rotates away from the second rod (it is repelled).

In the cradle method, what result shows that two charged rods carry opposite types of charge?

The suspended rod rotates towards the second rod (it is attracted).

True or False? In the cradle method, if the suspended rod is attracted to the second charged rod, the two rods must carry the same type of charge.

False. Attraction between the rods shows they carry opposite types of charge; only like charges cause repulsion.

Define an electric field .

An electric field is the region around a charged object in which another charge experiences a force.

Define a uniform electric field .

A uniform electric field is one in which the field lines are parallel and equally spaced , so the field strength is the same at every point.

In which direction do electric field lines point around an isolated point charge?

Away from positive charges and towards negative charges.

What does the direction of a field line at a given point represent?

The direction of the force that a positive charge would experience if placed at that point.

Field lines drawn close together show a ______ electric field, while field lines drawn far apart show a ______ electric field.

Field lines drawn close together show a strong electric field, while field lines drawn far apart show a weak electric field.

Describe the electric field lines between two oppositely charged parallel plates.

Parallel, straight lines directed from the positive plate to the negative plate — this is a uniform electric field.

Why are the field lines around a charged conducting sphere symmetrical, just like those around a point charge?

The charge spreads evenly over the sphere's surface, because like charges repel and the conducting surface allows them to move freely.

True or False? As the distance between two charged objects decreases, the electrostatic force between them becomes weaker.

False. The force becomes stronger as the distance decreases, and weaker as the distance increases.

Define an electrical conductor .

A conductor is a material that allows charge (usually electrons) to flow through it easily, e.g. copper, silver, aluminium, steel .

Define an electrical insulator .

An insulator is a material with no free charges, so it does not allow charge to flow through it easily, e.g. rubber, plastic, glass, wood .

Why do metals conduct electricity well, in terms of their atomic structure?

Metals consist of positive metal ions with their outermost electrons delocalised (free to move), so charge can flow easily through them.

What piece of apparatus can be used to test whether a material is a conductor or an insulator?

A gold-leaf electroscope (GLE) (or, alternatively, an electronic charge detector).

Describe the main parts of a gold-leaf electroscope.

A metal plate connected by a metal rod to a thin gold leaf , held by an insulating collar inside a box with glass sides .

In a gold-leaf electroscope test, what result shows that the tested material is a good conductor?

The gold leaf falls — charge flows away from the leaf through the material.

If the gold leaf falls ______ when a material touches the charged plate, that material is a poor conductor.

If the gold leaf falls slowly when a material touches the charged plate, that material is a poor conductor.

True or False? If the gold leaf remains sticking out when a material touches the charged plate of the electroscope, that material is a good conductor.

False. The leaf remaining in place shows the material is a poor conductor (good insulator) ; a good conductor causes the leaf to fall.

Current is the amount of charge passing a point in a circuit per second, measured in amperes (A) .

Charge, current and time are related by the equation: charge = current × ______ .

Charge, current and time are related by the equation: charge = current × time .

How is current measured, and how must the meter be connected in a circuit?

Current is measured using an ammeter , which must be connected in series with the part of the circuit being measured.

Define conventional current .

Conventional current is defined as the flow of charge from positive to negative , even though electrons actually flow from negative to positive.

True or False? In a metal, current is caused by a flow of free (delocalised) electrons.

True. In metals, the current is caused by a flow of free (delocalised) electrons .

What is the difference between direct current (d.c.) and alternating current (a.c.)?

A direct current (d.c.) is steady and always flows the same way around a circuit, from positive to negative. An alternating current (a.c.) continuously changes direction, going back and forth around the circuit.

What type of current do cells (batteries) produce, and what type does mains electricity supply?

Cells (batteries) produce direct current (d.c.) . Mains electricity supplies alternating current (a.c.) .

Define electromotive force (e.m.f.) .

Electromotive force (e.m.f.) is the electrical work done by a source in moving a unit charge around a complete circuit, measured in volts (V) .

Define potential difference (p.d.) .

Potential difference (p.d.) is the work done by a unit charge passing through a component, measured in volts (V) .

How does the energy transfer described by e.m.f. differ from that described by potential difference?

E.m.f. describes energy supplied to the charge carriers from the power source. Potential difference describes energy transferred from the charge carriers to a component.

How should a voltmeter be connected to measure the potential difference across a component?

A voltmeter is connected in parallel with the component being tested, with a connection to the two points between which the potential difference is being measured.

Voltmeters can be either ______ (with a needle and scale) or digital (with an electronic read-out).

Voltmeters can be either analogue (with a needle and scale) or digital (with an electronic read-out).

True or False? When several cells are connected in series, their combined e.m.f. is equal to the sum of their individual e.m.f.s.

True. The total e.m.f. of cells connected in series is equal to the sum of their individual e.m.f.s.

In a series circuit, how does the sum of the potential differences across the components compare with the e.m.f. of the power supply?

The sum of the potential differences across the components in a series circuit is equal to the total e.m.f. of the power supply.

Resistance is the opposition to current, measured in ohms (Ω) .

State Ohm's law in words.

Current is directly proportional to potential difference , provided the temperature remains constant.

For a given potential difference, the ______ the resistance, the lower the current.

For a given potential difference, the higher the resistance, the lower the current.

True or False? According to Ohm's law, the potential difference across a conductor decreases as its resistance increases, for a constant current.

False. The potential difference across a conductor increases as its resistance increases, for a constant current.

Define ohmic conductor .

An ohmic conductor (such as a resistor) has a constant resistance, so the current through it is directly proportional to the potential difference across it, at constant temperature.

Why does the current in a filament lamp increase at a slower rate than the potential difference as the p.d. across it is increased?

The current heats the filament , which increases its resistance . This opposes the current, causing it to increase at a slower rate.

A thermistor is a non-ohmic, temperature-sensitive resistor; its resistance depends on temperature, and it is used in circuits such as thermostats and temperature sensors.

True or False? As the temperature of a thermistor increases, its resistance increases.

False. As a thermistor's temperature increases, its resistance decreases (for a negative temperature coefficient thermistor).

Thermistors are used in temperature-sensing circuits such as ovens, fire alarms and digital ______ .

Thermistors are used in temperature-sensing circuits such as ovens, fire alarms and digital thermometers .

O LevelPhysicsCambridge (CIE)Flashcards4. Electricity & Magnetism4.2 Electrical Quantities

4.2 Electrical Quantities (Cambridge (CIE) O Level Physics): Flashcards

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Cards in this collection (56)

Define electric charge.
Electric charge is a property of matter that can be either positive or negative.
Electric charge is measured in units called ______.
Electric charge is measured in units called coulombs (C).
What type of force acts between two objects that carry the same type of charge?
A repulsive force — the objects push apart.
What type of force acts between two objects that carry opposite types of charge?
An attractive force — the objects pull towards each other.
True or False?
Two objects that are both negatively charged will attract each other when brought close together.
False.
Objects with the same charge (both negative, or both positive) repel; only objects with opposite charges attract.
Define electrostatic repulsion.
Electrostatic repulsion is the repulsive force that acts between two objects carrying the same type of charge.
Rubbing an insulating rod with a cloth transfers ______ from its surface, leaving the rod with an overall positive charge.
Rubbing an insulating rod with a cloth transfers electrons from its surface, leaving the rod with an overall positive charge.
In the cradle method for demonstrating electrostatic charge, how is the test material suspended?
By a length of thread (string) hung from a clamp stand, so that it can rotate freely.
In the cradle method, what result shows that two charged rods carry the same type of charge?
The suspended rod rotates away from the second rod (it is repelled).
In the cradle method, what result shows that two charged rods carry opposite types of charge?
The suspended rod rotates towards the second rod (it is attracted).
True or False?
In the cradle method, if the suspended rod is attracted to the second charged rod, the two rods must carry the same type of charge.
False.
Attraction between the rods shows they carry opposite types of charge; only like charges cause repulsion.
Define an electric field.
An electric field is the region around a charged object in which another charge experiences a force.
Define a uniform electric field.
A uniform electric field is one in which the field lines are parallel and equally spaced, so the field strength is the same at every point.
In which direction do electric field lines point around an isolated point charge?
Away from positive charges and towards negative charges.
What does the direction of a field line at a given point represent?
The direction of the force that a positive charge would experience if placed at that point.
Field lines drawn close together show a ______ electric field, while field lines drawn far apart show a ______ electric field.
Field lines drawn close together show a strong electric field, while field lines drawn far apart show a weak electric field.
Describe the electric field lines between two oppositely charged parallel plates.
Parallel, straight lines directed from the positive plate to the negative plate — this is a uniform electric field.
Why are the field lines around a charged conducting sphere symmetrical, just like those around a point charge?
The charge spreads evenly over the sphere's surface, because like charges repel and the conducting surface allows them to move freely.
True or False?
As the distance between two charged objects decreases, the electrostatic force between them becomes weaker.
False.
The force becomes stronger as the distance decreases, and weaker as the distance increases.
Define an electrical conductor.
A conductor is a material that allows charge (usually electrons) to flow through it easily, e.g. copper, silver, aluminium, steel.
Define an electrical insulator.
An insulator is a material with no free charges, so it does not allow charge to flow through it easily, e.g. rubber, plastic, glass, wood.
Why do metals conduct electricity well, in terms of their atomic structure?
Metals consist of positive metal ions with their outermost electrons delocalised (free to move), so charge can flow easily through them.
What piece of apparatus can be used to test whether a material is a conductor or an insulator?
A gold-leaf electroscope (GLE) (or, alternatively, an electronic charge detector).
Describe the main parts of a gold-leaf electroscope.
A metal plate connected by a metal rod to a thin gold leaf, held by an insulating collar inside a box with glass sides.
In a gold-leaf electroscope test, what result shows that the tested material is a good conductor?
The gold leaf falls — charge flows away from the leaf through the material.
If the gold leaf falls ______ when a material touches the charged plate, that material is a poor conductor.
If the gold leaf falls slowly when a material touches the charged plate, that material is a poor conductor.
True or False?
If the gold leaf remains sticking out when a material touches the charged plate of the electroscope, that material is a good conductor.
False.
The leaf remaining in place shows the material is a poor conductor (good insulator); a good conductor causes the leaf to fall.
Define current.
Current is the amount of charge passing a point in a circuit per second, measured in amperes (A).
Charge, current and time are related by the equation: charge = current × ______.
Charge, current and time are related by the equation: charge = current × time.
How is current measured, and how must the meter be connected in a circuit?
Current is measured using an ammeter, which must be connected in series with the part of the circuit being measured.
Define conventional current.
Conventional current is defined as the flow of charge from positive to negative, even though electrons actually flow from negative to positive.
True or False?
In a metal, current is caused by a flow of free (delocalised) electrons.
True.
In metals, the current is caused by a flow of free (delocalised) electrons.
What is the difference between direct current (d.c.) and alternating current (a.c.)?
A direct current (d.c.) is steady and always flows the same way around a circuit, from positive to negative. An alternating current (a.c.) continuously changes direction, going back and forth around the circuit.
What type of current do cells (batteries) produce, and what type does mains electricity supply?
Cells (batteries) produce direct current (d.c.). Mains electricity supplies alternating current (a.c.).
Define electromotive force (e.m.f.).
Electromotive force (e.m.f.) is the electrical work done by a source in moving a unit charge around a complete circuit, measured in volts (V).
Define potential difference (p.d.).
Potential difference (p.d.) is the work done by a unit charge passing through a component, measured in volts (V).
How does the energy transfer described by e.m.f. differ from that described by potential difference?
E.m.f. describes energy supplied to the charge carriers from the power source. Potential difference describes energy transferred from the charge carriers to a component.
How should a voltmeter be connected to measure the potential difference across a component?
A voltmeter is connected in parallel with the component being tested, with a connection to the two points between which the potential difference is being measured.
Voltmeters can be either ______ (with a needle and scale) or digital (with an electronic read-out).
Voltmeters can be either analogue (with a needle and scale) or digital (with an electronic read-out).
True or False?
When several cells are connected in series, their combined e.m.f. is equal to the sum of their individual e.m.f.s.
True.
The total e.m.f. of cells connected in series is equal to the sum of their individual e.m.f.s.
In a series circuit, how does the sum of the potential differences across the components compare with the e.m.f. of the power supply?
The sum of the potential differences across the components in a series circuit is equal to the total e.m.f. of the power supply.
Define resistance.
Resistance is the opposition to current, measured in ohms (Ω).
State Ohm's law in words.
Current is directly proportional to potential difference, provided the temperature remains constant.
Write the equation linking resistance, potential difference and current, in symbol form.
$R = \frac{V}{I}$
For a given potential difference, the ______ the resistance, the lower the current.
For a given potential difference, the higher the resistance, the lower the current.
True or False?
According to Ohm's law, the potential difference across a conductor decreases as its resistance increases, for a constant current.
False.
The potential difference across a conductor increases as its resistance increases, for a constant current.
Describe the circuit set-up used to determine the resistance of a component.
A power supply (set to a low voltage, typically 1–2 V), an ammeter connected in series, and a voltmeter connected in parallel with the component. The current and potential difference readings are substituted into $R = \frac{V}{I}$ to find the resistance.
A charge of 5.0 C passes through a resistor at a constant rate in 3.0 s. The potential difference across the resistor is 2.0 V. Calculate the resistance.
$I = \frac{Q}{t} = \frac{5.0}{3.0} = 1.67 A$
$R = \frac{V}{I} = \frac{2.0}{1.67} = 1.2 Ω$
How does the resistance of a wire vary with its length?
Resistance is directly proportional to length: $R \propto L$
How does the resistance of a wire vary with its cross-sectional area?
Resistance is inversely proportional to cross-sectional area: $R \propto \frac{1}{A}$
Define ohmic conductor.
An ohmic conductor (such as a resistor) has a constant resistance, so the current through it is directly proportional to the potential difference across it, at constant temperature.
Why does the current in a filament lamp increase at a slower rate than the potential difference as the p.d. across it is increased?
The current heats the filament, which increases its resistance. This opposes the current, causing it to increase at a slower rate.
Define thermistor.
A thermistor is a non-ohmic, temperature-sensitive resistor; its resistance depends on temperature, and it is used in circuits such as thermostats and temperature sensors.
True or False?
As the temperature of a thermistor increases, its resistance increases.
False.
As a thermistor's temperature increases, its resistance decreases (for a negative temperature coefficient thermistor).
Thermistors are used in temperature-sensing circuits such as ovens, fire alarms and digital ______.
Thermistors are used in temperature-sensing circuits such as ovens, fire alarms and digital thermometers.
In a circuit where a thermistor is connected in series with a fixed resistor R, what happens to the potential difference across the thermistor when its temperature decreases?
As temperature decreases, the thermistor's resistance increases. Since the current I is the same throughout a series circuit, and $V = I R$ , the potential difference across the thermistor increases.

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