Energy Transfers in Circuits (Edexcel GCSE Physics): Flashcards
Exam code: 1PH0
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- FrontHeating in Circuits
Define the heating effect of current.
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Cards in this collection (45)
Define the heating effect of current.
When charge passes through a component, some of the energy is transferred from the electrons to the component by heating, increasing its temperature.
By what three processes is thermal energy dissipated into the surroundings?
By thermal conduction, convection and radiation.
State one advantage and one danger of the heating effect of an electric current.
Advantage: it is used in devices such as electric heaters.
Danger: if too much current flows through a component, the heating effect can be dangerous, causing burns or a fire.
What two factors determine the amount of heat produced in a component carrying a current?
The current through it (a greater current produces more heat) and its resistance (a higher resistance produces more heat for a given current).
Wasted thermal energy makes a device less ______.
Wasted thermal energy makes a device less efficient.
True or False?
Reducing the resistance of a circuit always reduces the amount of heat produced.
False.
Reducing resistance can cause the current to increase, which could actually increase the amount of heat produced.
Why does a metal conductor heat up when a current flows through it?
The flowing electrons collide with the ions in the metal lattice, transferring energy to the ions and causing them to vibrate more.
Define current in a metal conductor.
Current is the flow of electrons through the metal conductor.
Name three appliances that use the heating effect of an electric current.
Any three of: electric heaters, electric ovens, electric hobs, toasters, kettles.
The heat produced in wires can be reduced by reducing the ______ or by using wires with a lower resistance.
The heat produced in wires can be reduced by reducing the current or by using wires with a lower resistance.
Why is copper commonly used for electrical wiring?
Copper has a relatively low resistance and is fairly cheap. Lower-resistance alternatives exist but are more expensive.
True or False?
Using wires with a higher resistance would reduce the amount of heat produced in a circuit.
False.
Using wires with a lower resistance reduces the amount of heat produced.
Name four appliances that make use of the heating effect of current as an advantage.
Electric kettles, electric ovens, domestic heating and electric toasters.
How does the heating effect of current reduce the efficiency of a device?
Some electrical energy is transferred as waste heat rather than usefully, for example waste heat in a light bulb or overheating in a computer.
How can the heating effect of current pose a fire hazard?
Too much current passing through low-quality wiring can cause sparks or excessive heat, for example in an electric motor, which can start a fire.
Many domestic fires are caused by too much current passing through low-quality ______.
Many domestic fires are caused by too much current passing through low-quality wiring.
What energy transfer takes place in a kettle?
A kettle converts electrical work to a thermal energy store.
True or False?
Waste heat produced in a light bulb is an example of the heating effect being used as an advantage.
False.
Waste heat in a light bulb is a disadvantage — it reduces the efficiency of the device.
Define work done in an electrical circuit.
Work done is done when charge flows through a circuit, and is equal to the energy transferred.
What three quantities does the energy transferred by electrical work in a component depend on?
The current, the potential difference and the amount of time the component is used for.
State the two equations used to calculate electrical energy transferred.
E = P × t
E = I × V × t
When charge flows around a circuit, the energy supplied by the battery is equal to the energy transferred to all the ______ in the circuit.
When charge flows around a circuit, the energy supplied by the battery is equal to the energy transferred to all the components in the circuit.
Calculate the energy transferred in 1 minute when a current of 0.7 A passes through a potential difference of 4 V.
E = I × V × t = 0.7 × 4 × 60 = 168 J
True or False?
The time t in the electrical energy equations can be entered in minutes.
False.
The time t must always be converted into seconds before it is used in the equations.
Define power.
The energy transferred per second (or per unit time), measured in watts.
1 kilowatt (1 kW) is equal to ______ watts.
1 kilowatt (1 kW) is equal to 1000 watts.
What is 1 watt equivalent to, in joules per second?
1 W = 1 J s⁻¹.
State the equation that links power, energy transferred (or work done) and time.
P = E/t (or P = W/t), where E or W is in joules, t is in seconds and P is in watts.
Calculate the energy transferred if an iron of power 2000 W is used for 5 minutes.
t = 5 × 60 = 300 s
E = Pt = 2000 × 300 = 600 000 J
True or False?
A 3 kW appliance always transfers more total energy than a 1 kW appliance.
False.
The total energy transferred also depends on how long each appliance is used for, not just its power.
Define electrical power.
The rate of energy transfer, or the amount of energy transferred per second.
What two quantities does the power of an electrical device depend on?
The voltage (potential difference) of the device and the current of the device.
State the equation linking power, current and voltage, and give the unit of each quantity.
P = IV, where P is power in watts, I is current in amps and V is voltage in volts.
Combining the equations P = IV and V = IR gives power in terms of resistance: P = ______.
Combining the equations P = IV and V = IR gives power in terms of resistance: P = _I_^2^_R_.
Calculate the potential difference across a 48 W electric motor carrying a current of 4 A.
V = P/I = 48/4 = 12 V
Calculate the power dissipated by a 20 Ω resistor carrying a current of 6 A.
P = I2R = (6)2 × 20 = 720 W
True or False?
You should always use P = I2R to calculate power, regardless of the values given in the question.
False.
Which power equation to use depends on whether the current or the voltage has been given in the question.
Define power.
Power is the amount of energy an appliance transfers electrically every second.
What two factors determine the amount of energy an appliance transfers?
The time the appliance is switched on for, and the power of the appliance.
A 1 kW iron uses the same amount of energy in 1 hour as a 2 kW iron uses in ______.
A 1 kW iron uses the same amount of energy in 1 hour as a 2 kW iron uses in 30 minutes.
As charge flows around a circuit, how is energy transferred between the power source, the electrons and the components?
Energy is transferred to the electrons at the power source, then from the electrons to the components as they pass through each one.
Name three appliances that use an electric motor, and state what the motor does in each.
Vacuum cleaner – creates suction to remove dust and dirt.
Washing machine – rotates the drum to wash or dry clothes.
Refrigerator – compresses the refrigerant, which is used to remove heat from inside the fridge.
Name three appliances that use a heating element, and state what each is used for.
Toaster – toasts bread.
Kettle – boils water.
Electric heater – heats a room using an electrical heating element.
What three pieces of information does an appliance's power label usually show?
The potential difference required (e.g. 230 V), the frequency of the supply (e.g. 50 Hz) and the power rating in watts.
True or False?
A higher power rating means an appliance changes its stored energy more slowly.
False.
A higher power rating means the appliance changes its stored energy more quickly — for example, a 2000 W kettle transfers 2000 J of energy every second.
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