Topic 2 - Electrical Energy Flashcards
Focus 1
Define energy.
Energy is the ability to do work, and can be either potential or kinetic.
Focus 1
Describe how electrical energy can be transformed into other forms.
Electrical energy can be transformed into other forms of energy, for example:
Electrical energy (power source) → (appliance e.g. toaster) → heat & light energy
Focus 1
Define electric current.
Current is the flow of electrical charge; a measure of the amount of electric charge passing through a point in a circuit per second
In an electric circuit, the charge is usually carried by electrons
Although the charge carrier can be any charged particle such as a proton or ion
Current is measured in amps and is represented by “I”
Focus 2
What is the relationship between “like” and “unlike” charges?
All electrically charged objects have an electric field around them.
Like charges (e.g. + and + ; - and - ) repel each other
Unlike charges (e.g. + and - ) attract each other
Focus 2
What are electric fields?
A field is the area around an object where a force is exerted on another object, usually without there being any contact between the objects.
Fields can be represented as lines which show the direction of the force experienced by another object in the field.
An electric field applied to some material will cause electric current to flow through that material.
In an electric field, a charged object or particle experiences a force; if the forces acting on any object are unbalanced (unequal amount of + and - charged), it will cause the object to move / accelerate.
Focus 2
Explain how an electric field provides a voltage (potential difference) that produces a current when there is a closed circuit.
Electric fields cause objects to move / accelerate (causing a change in energy), therefore providing a voltage (potential difference)
Voltage is the change in energy across an electric system
The voltage in the electrical system (the change in energy caused by the electric field) for example in the power source (e.g. battery, which has a positive and negative terminal) produces a current (the flow of electrons) in a closed circuit
Focus 3
Define Current.
Current = the flow of electrons through a circuit / the rate of flow of electron charge past a point
Measured in Amps, by using an Ammeter.
The Ammeter should be set up in series with the circuit.
Symbol in equations is I
Focus 3
Define Voltage.
Voltage = the change in energy in an electrical system / electric potential energy per unit charge
Measured in Volts; a Voltmeter is used to measure the potential difference across different parts of a circuit
The Voltmeter should be set up in parallel with the part of the circuit across which the voltage is being measured
Symbol in equations is V
Focus 3
Define Resistance.
Resistance = the measure of opposition to the flow of electric charge in a circuit
Measured in Ohms
Focus 3
Describe Ohm’s Law.
Ohm’s law is a formula used to calculate the relationship between voltage, current, and resistance in an electrical circuit.
Voltage = Current x Resistance
Volts = Amps x Ohms
V = I x Ω
I = V/R
R = V/I
Focus 4
Describe series circuits.
Circuit that is arranged in a continuous path so that the current only has one path to take (the current is the same at every point in the circuit)
The electric current (charge flowing) must flow through each resistor (e.g. light bulbs) one after the other
The total resistance of the circuit can be found by adding up the resistance of all the parts of a circuit
The amount of current in the circuit can be determined using Ohm’s law V = IR (or I = V/R)
The source voltage is shared between the parts of a circuit; the greater the resistance of a part of the circuit the greater its share of the voltage
Focus 4
Describe parallel circuits.
A circuit in which the current breaks up, with some current flowing along each parallel branch / path and re-combining when the branches region (meet up again)
The current (electron flow) will take the path of least resistance
Focus 5
Define Work.
Work = the transfer of energy
Work is done on an object when energy is transferred to an object
SI unit for work = joule (J)
Focus 5
Define Energy.
Energy = the ability of a body or system to do work and produce a change
Energy can be potential or kinetic
SI unit for energy = joule (J)
Focus 5
Define Power.
Power = the amount of energy that can be produced in a given amount of time
It is the rate of doing work
Power = amount of energy consumed per unit time
Power = energy / time
SI unit for power = joules per second or in electricity Watts
Focus 5
Define Electrical Power.
Electrical power = the rate of energy consumption in an electrical circuit
Power = Voltage x Current
P = V x I
Watts = Volts x Amps
Focus 5
Recall the law of conservation of energy.
Energy can neither be created nor destroyed, it can only be transformed from one form to another.
Focus 5
Relate power and energy to voltage and current.
Energy = Power x time
Energy = Voltage x Current x time
E = V x I x time
Example: if a device that uses 1 kW of power is used for 1 hour, it has used 1 kWhr of electrical energy
Focus 5
Why are kWh units are used to measure household electricity?
Measured in kWhr rather than joules because the unit of joules is very small
1 Watt second = 1 joule per second x 1 second
1 kWhr = 1000 joules per second x (60 x 60) seconds
= 3 600 000 joules
Focus 5
Explain why parts of household circuits are connected in parallel while others are in series.
In a series circuit, every device must function for the circuit to be complete.
E.g. if one light bulb is turned off / is broken, the whole circuit won’t function.
In a parallel circuit, each device has its own circuit.
E.g. if one lightbulb is turned off / is broken, the rest of the light bulbs will continue to function.
Focus 6
Explain how short circuits occur.
Occurs when a conductor is introduced into the circuit, so that there is an unintentional low resistance pathway across the voltage source.
Electrons will take the path of least resistance.
This results in very high and possibly unsafe electrical currents.
Focus 6
Explain how short circuits can lead to safety issues.
High currents caused by short circuits can produce heat in conductors which can lead to fires.
High currents can result in objects becoming “live” (electrically charged) which can lead to electric shocks and electrocution.
Focus 6
Explain how a fuse could be used to protect people from short circuits.
A fuse is a device placed in series in a circuit to protect it from high currents.
It works by heating up and burning when a predetermined level of current is reached.
When it burns, it breaks the circuit so no further current flows, protecting people from high currents.
Focus 6
Explain how a circuit breaker could be used to protect people from short circuits.
Circuit breakers are switches that are operated by an electromagnet.
When a predetermined level of current is reached, the electromagnet has enough energy to trip the switch and break the current, protecting people from high currents.
