IGCSEScienceCambridge (CIE)Co-ordinated Sciences (Double Award)PhysicsFlashcards4. Electricity & MagnetismElectrical Quantities

Electrical Quantities (Cambridge (CIE) IGCSE Co-ordinated Sciences (Double Award): Physics): Flashcards

Exam code: 0654 & 0973

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  • FrontElectric Charge

    How many types of electric charge are there?

Cards in this collection (86)

  • How many types of electric charge are there?

    There are two types of electric charge: positive and negative.

  • What are the charges of the particles inside an atom?

    • Electrons are negatively charged

    • Protons are positively charged

    • Neutrons are neutral (no charge)

  • Why is the overall charge of an atom zero?

    An atom contains equal numbers of protons and electrons, so their equal and opposite charges cancel out.

  • True or False?

    Opposite charges attract.

    True.

    Opposite charges attract each other.

  • What happens when two like charges are brought close together?

    When two like charges are brought close together, they repel each other.

  • What units is electric charge measured in? (Extended Tier Only)

    Electric charge is measured in coulombs (C).

  • What is the purpose of rubbing insulating solids with a cloth in electrostatic experiments?

    Rubbing transfers electrons between the cloth and the insulator, leaving them with opposite net charges.

  • When charging by friction, why does one insulator become positively charged?

    Only electrons can move. The insulator that loses electrons is left with a net positive charge, while the insulator that gains electrons becomes negatively charged.

  • Why does charge remain on an insulator after it has been charged by friction?

    The charges cannot immediately flow away, because insulators do not conduct.

  • Give two simple methods of showing that an object is electrically charged.

    Any two from:

    • using it to pick up small pieces of paper

    • sticking a charged balloon to a wall by attraction

    • using it to pull a stream of water towards it

    • bringing it close to another charged rod

  • Describe an experiment to demonstrate electrostatic charging by friction.

    • Suspend an insulating rod in a cradle using a length of thread so it can rotate freely

    • Rub one end of the rod with a cloth to give it a charge

    • Charge one end of a second insulating rod by rubbing it with a cloth

    • Hold the charged end of the second rod close to the charged end of the first rod and observe whether it attracts or repels

  • How can you determine whether two charged rods have the same charge?

    Observe their interaction when brought close together.

    • If they repel each other, they have the same charge

    • If they attract each other, they have opposite charges

  • Why can a negatively charged comb pick up small, uncharged pieces of paper?

    The positive charges in the paper are attracted to the surface closest to the comb. Opposite charges attract, so the paper sticks to the comb due to electrostatic attraction.

  • Define electric field. (Extended Tier Only)

    An electric field is a region of space in which an electric charge experiences a force.

  • How is the direction of an electric field at a point defined? (Extended Tier Only)

    The direction of an electric field at a point is the direction of the force on a positive charge at that point.

  • True or False?

    Electric fields always point towards positive charges. (Extended Tier Only)

    False.

    The direction of an electric field is the direction of the force on a positive charge, so electric fields point away from positive charges and towards negative charges.

  • What creates an electric field? (Extended Tier Only)

    Charged objects create electric fields around themselves, similar to how magnets create magnetic fields.

  • Why is an electric field a vector quantity? (Extended Tier Only)

    An electric field has both magnitude (strength) and direction.

  • Define conductor.

    A conductor is a material that allows charge (usually electrons) to flow through it easily.

  • True or False?

    Metals are generally good insulators.

    False.

    The best conductors tend to be metals.

  • Why do metals conduct electricity very well?

    • Metals are made up of positively charged metal ions with their outermost electrons delocalised, meaning the electrons are free to move

    • Current is the rate of flow of electrons, so the more easily electrons are able to flow, the better the conductor

  • Define insulator.

    An insulator is a material that has no free charges, so it does not allow charge to flow through it very easily.

  • True or False?

    Insulators allow no charge at all to pass through them.

    False.

    Some non-metals, such as wood, allow some charge to pass through them. Insulators can conduct a little in the form of static electricity.

  • Give two examples of electrical conductors and two examples of electrical insulators.

    Conductors — any two from:

    • silver

    • copper

    • aluminium

    • steel

    Insulators — any two from:

    • rubber

    • plastic

    • glass

    • wood

  • Define current.

    Current is the rate of flow of electric charge.

  • What is the purpose of an ammeter?

    The purpose of an ammeter is to measure the current in a circuit.

  • True or False?

    Ammeters should be connected in parallel to measure current.

    False.

    Ammeters should be connected in series with the component being measured.

  • Which is more accurate, a digital or an analogue ammeter?

    A digital ammeter is more accurate than an analogue ammeter because it gives a specific value, is capable of displaying more precise values and can measure very small currents.

  • In metal wires, the current is a flow of negatively charged ______. (Extended Tier Only)

    In metal wires, the current is a flow of negatively charged electrons.

  • What is the equation relating current, charge and time? (Extended Tier Only)

    The equation relating current, charge and time is:

    I = \frac{Q}{t}

    Where:

    • I = current, measured in amps (A)

    • Q = charge, measured in coulombs (C)

    • t = time, measured in seconds (s)

  • Define conventional current. (Extended Tier Only)

    Conventional current is the flow of positive charge, from the positive terminal to the negative terminal of a cell.

  • How is electron flow different to conventional current? (Extended Tier Only)

    Electrons flow from the negative terminal to the positive terminal of a cell. This is the opposite direction to conventional current.

  • Define direct current (d.c.).

    Direct current (d.c.) is a steady current, constantly flowing in the same direction in a circuit, from positive to negative.

  • Define alternating current (a.c.).

    Alternating current (a.c.) is a current that continuously changes its direction, going back and forth around a circuit.

  • Sketch the graphs for d.c. and a.c.

    The graphs for d.c. and a.c. are

    Graphs of Direct Current (D.C.) and Alternating Current (A.C.). The D.C. graph shows a constant current over time, while the A.C. graph shows a sinusoidal wave varying over time.

  • True or False?

    Cells and batteries are sources of d.c.

    True.

    Cells and batteries produce direct current (d.c.), while electrical generators, such as mains electricity, produce alternating current (a.c.).

  • True or False?

    An a.c. power source involves a positive and negative terminal.

    False.

    An a.c. power source involves two identical terminals that change from positive to negative and back again.

  • Name three sources that supply a voltage to a circuit.

    Three sources that supply a voltage to a circuit are:

    • a cell

    • a battery (multiple cells)

    • an electrical generator

  • What is another name for voltage?

    Voltage is also known as potential difference (p.d.).

  • The voltage of a source causes a ______ to flow in the circuit.

    The voltage of a source causes a current to flow in the circuit.

  • True or False?

    Voltage is measured in amperes.

    False.

    Voltage is measured in volts (V).

  • How is voltage shared in a series circuit?

    In a series circuit, the voltage of the source is shared between the components.

    The sum of the voltages across the individual components is equal to the total voltage of the power supply. If the components have equal resistance, the voltage is shared equally.

  • Define voltmeter.

    A voltmeter is a device used to measure the voltage (potential difference) between two points in a circuit.

  • True or False?

    Voltmeters are connected in series with the component being measured.

    False.

    Voltmeters are connected in parallel with the component being measured. This is because voltage is the difference in electrical potential between two points in a circuit.

  • True or False?

    Electromotive force (e.m.f.) is the potential difference of the power source in a circuit. (Extended Tier Only)

    True.

    Electromotive force (e.m.f.) is the name given to the potential difference of the power source in a circuit.

  • Define electromotive force (e.m.f.). (Extended Tier Only)

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

  • Define potential difference. (Extended Tier Only)

    Potential difference is the work done by a unit charge passing between two points in a circuit.

  • True or False?

    Potential difference is measured in amperes. (Extended Tier Only)

    False.

    Potential difference is measured in volts (V).

  • True or False?

    Resistance is a measure of how difficult it is for current to pass through a conductor or component.

    True.

    Resistance is the opposition to current. The higher the resistance of a circuit, the lower the current.

  • What is the equation for Ohm's law?

    The equation for Ohm's law is: R = \frac{V}{I}

    Where:

    • R = resistance, measured in ohms (Ω)

    • V = potential difference, measured in volts (V)

    • I = current, measured in amperes (A)

  • True or False?

    The unit of resistance is volts.

    False.

    The unit of resistance is the ohm, represented by the Greek letter omega (Ω).

  • What is an I-V graph? (Extended Tier Only)

    An I-V graph, or current-voltage graph, shows the relationship between the current flowing through a component and the potential difference across it.

  • What is the shape of the I-V graph for a wire or fixed resistor? (Extended Tier Only)

    The I-V graph for a wire or fixed resistor (at constant temperature) is a straight line passing through the origin. Current is directly proportional to potential difference, so the resistance is constant. These components are known as ohmic resistors.

  • True or False?

    The resistance of a non-ohmic resistor is constant. (Extended Tier Only)

    False.

    A non-ohmic resistor has a resistance that is not constant, so its I-V graph is not a straight line.

  • State the independent and dependent variables in the investigation of how the length of a wire affects its resistance.

    In this investigation:

    • the independent variable is the length of the resistance wire

    • the dependent variable is the resistance of the wire

  • State two control variables in the investigation of how the length of a wire affects its resistance.

    • the voltage of the power supply

    • the temperature of the wire

  • In the resistance investigation, the length of the wire between the crocodile clips is measured using a ______.

    In the resistance investigation, the length of the wire between the crocodile clips is measured using a metre rule.

  • How is the resistance of each length of wire calculated in the resistance investigation?

    The resistance of each length of wire is calculated using the equation R = \frac{V}{I}, where the voltage V is measured using a voltmeter and the current I is measured using an ammeter.

  • Describe the expected graph of resistance against length for a wire at constant temperature.

    The graph is a straight line through the origin with a positive correlation — the longer the wire, the higher its resistance.

  • True or False?

    The temperature of the wire must be kept constant throughout the resistance investigation.

    True.

    Keeping the temperature of the wire constant ensures its resistance stays constant. This is done by using low values of current and switching off the current between readings.

  • How can zero errors be avoided in the resistance investigation?

    • ensure the first crocodile clip starts at 0 on the metre rule

    • ensure the ammeter and voltmeter both start from zero

  • State one safety precaution that should be taken when investigating the resistance of a wire.

    Any one from:

    • never touch the wire directly when the circuit is switched on, as it can become very hot

    • switch off the power supply immediately if burning is smelled

    • keep liquids away from the electrical equipment

  • Define the resistance of a wire. (Extended Tier Only)

    The resistance of a wire is the opposition to the flow of electrons as they pass through the wire, caused by their collisions with the metal ions in the wire.

  • How does the length of a wire affect its resistance? (Extended Tier Only)

    The resistance of a wire is directly proportional to its length. This means that as the length of the wire increases, its resistance also increases by the same factor.

  • How does the cross-sectional area of a wire affect its resistance? (Extended Tier Only)

    The resistance of a wire is inversely proportional to its cross-sectional area. As the wire's cross-sectional area (thickness) increases, its resistance decreases, and vice versa.

  • True or False?

    If a wire is thicker, its resistance is greater. (Extended Tier Only)

    False.

    If a wire is thicker (greater diameter), there is more space for the electrons to flow through, so its resistance is smaller.

  • True or False?

    If a wire is longer, its resistance is higher. (Extended Tier Only)

    True.

    If a wire is longer, each electron will collide with more metal ions along the wire's length, resulting in a greater opposition to the flow of electrons.

  • If the length of a wire is increased by a factor of 3, what is the effect on its resistance? (Extended Tier Only)

    The resistance of a wire is directly proportional to its length, so if the length is increased by a factor of 3, the resistance will also increase by a factor of 3.

  • If the cross-sectional area of a wire is halved, what is the effect on its resistance? (Extended Tier Only)

    The resistance of a wire is inversely proportional to its cross-sectional area, therefore if its cross-sectional area is halved, its resistance will double.

  • Define electrical energy.

    Electrical energy is the energy transferred by an electric current.

    It is transferred from a power source to the components in a circuit, where it is transferred to other stores of energy, such as thermal or kinetic stores.

  • True or False?

    The energy transferred in a circuit is related to potential difference, current and time.

    True.

    The energy transferred is related to potential difference, current and time, as described by the equation E = V \times I \times t.

  • What is the electrical energy equation?

    The electrical energy equation is E = V \times I \times t, where:

    • E = energy transferred, measured in joules (J)

    • V = potential difference, measured in volts (V)

    • I = current, measured in amps (A)

    • t = time, measured in seconds (s)

  • How is energy transferred in a circuit?

    Energy is transferred from the power source to the components connected in the circuit:

    • as charge passes through the power supply, energy is transferred to the charge

    • as the charge passes through each component, energy is transferred from the charge to the component

  • What two factors affect the amount of energy transferred by an electrical appliance?

    The amount of energy transferred by an electrical appliance depends on:

    • how long the appliance runs for

    • the power rating of the appliance

  • True or False?

    Energy in a circuit is transferred from the power source to the components and the surroundings.

    True.

    Energy is transferred from the power source to the components, which often dissipate some of that energy to the surroundings.

  • What is the main energy transfer in a toaster while it toasts a slice of bread?

    Energy is transferred electrically from the mains supply to the thermal store of the heating element, which heats up the bread.

  • What is the main energy transfer in a washing machine during a washing cycle?

    Energy is transferred electrically from the mains supply to the kinetic store of the motor, which rotates the drum.

  • Define electrical power.

    Electrical power is the rate at which energy is transferred by an appliance. It is measured in watts (W).

  • True or False?

    Power is the rate of doing work.

    True.

    Power is defined as the rate of doing work, or the rate of energy transfer. It is measured in watts (W).

  • What is the electrical power equation?

    The electrical power equation is P = I \times V, where:

    • P = power, measured in watts (W)

    • I = current, measured in amps (A)

    • V = potential difference, measured in volts (V)

  • State the equation for power in terms of work done.

    The equation for power in terms of work done is P = \frac{W}{t}, where:

    • P = power, measured in watts (W)

    • W = work done, which is equivalent to energy transferred, measured in joules (J)

    • t = time, measured in seconds (s)

  • True or False?

    The unit of power is joules (J).

    False.

    The unit of power is watts (W), where 1 watt is equivalent to 1 joule per second (J/s).

  • What does the unit kilowatt-hour (kW h) mean?

    The kilowatt-hour (kW h) is a unit of energy. It is the energy transferred by 1 kilowatt of power used for 1 hour.

    It is mostly used to measure energy usage in homes, businesses and factories.

  • True or False?

    Energy usage in homes is measured in joules (J).

    False.

    Energy usage in homes is commonly measured in kilowatt-hours (kW h), because the energy transferred by household appliances measured in joules would be an inconveniently large number.

  • What is the equation for energy transferred in kilowatt-hours (kW h)?

    The equation for energy transferred in kilowatt-hours is E = P \times t, where:

    • E = energy transferred, measured in kilowatt-hours (kW h)

    • P = power, measured in kilowatts (kW)

    • t = time, measured in hours (h)

  • How many joules are there in 1 kilowatt-hour (kW h)?

    There are 3.6 \times 10^{6} joules in 1 kilowatt-hour:

    1 \text{ kW h} = 1000 \text{ W} \times 3600 \text{ s} = 3.6 \times 10^{6} \text{ J}

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