 The unit of current is Amperes.

# Electricity - Electrical Circuits 1

This Physics quiz is called 'Electricity - Electrical Circuits 1' and it has been written by teachers to help you if you are studying the subject at senior high school. Playing educational quizzes is one of the most efficienct ways to learn if you are in the 11th or 12th grade - aged 16 to 18.

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Electrical current flows in a closed path known as an electrical circuit. When a circuit is 'broken' it means that there is a gap which is stopping current from flowing. The break could be caused by a damaged component or wire, a component or connection that has become disconnected, or where there is a switch.

Understanding the basic principles associated with electrical circuits is useful as it allows you to predict how circuits behave. If you learn a few simple equations, you will be able work out a wide variety of important values relating to circuits and components. By now, you should be very familiar with Ohm's law (V = I R) and have had plenty of opportunity to use it, but there are some other vital relationships related to electrical current and electrical circuits that you should know in senior high school.

Electrical current is a flow of electrons. Each electron carries a small amount of charge and if there are enough electrons on the move, the amount of charge is useful. The unit of electrical charge is the coulomb (C) and if you have one coulomb of charge passing a given point in an electrical circuit per second, then a current of one amp is flowing. Two coulombs per second is two amps, five coulombs in a second is a current of five amps and so on. If you have ten coulombs flowing past in five seconds, that boils down to two coulombs per second, so the current is two amps. The current is worked out from the quantity of charge flowing divided by the number of seconds it takes it to pass a defined point in a circuit.

Moving electrical charge through a circuit needs work to be done - the greater the resistance, the greater the energy required. The energy is supplied by the power source for the electrical circuit. As the charge moves through the circuit, some of the energy it carries is transferred. In the wires, it is transferred to heat and wasted. In a component such as an LED, it is transferred into heat and also directly into light, which is the useful energy. Electrical potential difference is a measure of the energy transferred as the charge passes through a component and has the units of volts (V). One volt of electrical potential difference represents one coulomb of charge gaining or losing one joule of energy.

When you plot a graph of the current flowing through a component against the electrical potential difference, you end up with a current-potential difference graph. When asked about electricity in senior high school, you should be able to recognize the shapes of graphs for a resistor at constant temperature, a diode and a filament lamp. The examiners may put one in for a component for which you have never seen the graph, but you will be told what it is and be asked some simple questions about the information you can get from it.

1.
What is potential difference?
Work done per coulomb of charge that passes between two points
Kinetic energy per coulomb of charge that passes between two points
Work done per coulomb of charge that passes between three points
Work done per ampere of current that passes between two points
Strictly speaking, it should really be called electrical potential difference but at senior high school, potential difference is acceptable, when used in the correct context
2.
What is the formula for potential difference?
V = WQ
V = W2Q
V = 3W2Q
V = 5W3Q
V is in volts when W is in joules and Q is in coulombs
3.
What does the size of the electric current depend on?
The rate of flow of electric charge
The rate of flow of protons
The rate of flow of neutrons
All of the above
High currents = bigger flow rates
4.
What is the unit of charge?
Volts
Ohms
Coulombs
Amperes
The coulomb is the unit of charge. It is denoted by a C after a value of charge and is named for the French scientist Charles-Augustin de Coulomb who carried out a lot of pioneering work on electrical charge and magnetism
5.
What is the size of the current in a circuit if the charge, Q, is 100 C and lasts for 25 seconds?
1A
2A
3A
4A
Remember the definition - current is a measure of how much charge flows past a given point in one second. This should help you to get the right answer even if you can't recall the equation
6.
What is electrical current?
Flow of electric charge
Flow of protons
Flow of neutrons
Flow of water
Current is the flow of electric charge around a circuit. The charge is carried by electrons which are emitted by the negative electrode of the cell and travel to the positive electrode of the cell through the circuit
7.
What is the unit of current?
Volts
Ohms
Amperes
Joules
Amperes or Amps for short is the unit of current. It is usually denoted with an A after a value of current
8.
Which formula calculates the size of the current?
I = Q x t
I = Qt
I = tQ
Q = It
If you didn't remember the equation, you can work it out. Whenever you need to calculate the rate of something in physics, it is expressed as something per second. To get the 'per second' bit, you know that you need to divide by time. That eliminates two of the alternative answers so the one that works out the current must be the correct one
9.
What can be calculated from current-potential difference graphs?
Resistivity
Magnetism
Resistance
None of the above