Slides in this set
Charge / Current / Voltage / Resistance
The charge is the amount of electricity travelling through a circuit
The symbol for charge is Q
The unit for charge is coulombs
A capacitor is a device that stores charge
Charge (Q) = current (I) x time (t)
This is the flow of electrons round the circuit. This is measured in amps (I) Voltage
This is the driving force that pushes the current round. This is measured in volts (V)
This is anything in the circuit that slows the flow of current down. This is measured in ohms (W)
Ohm's Law shows that:
Voltage (V) = Current (I) x Resistance (R)
So if you increase the resistance then less current will flow if the voltage remains constant.
If you increase the voltage then more current will flow, if the resistance is constant.…read more
This is the idea that magnetism can travel from one object to
another even though they are insulated. An example of how
magnetic induction is used is in transformers. Two coils of wire are
wrapped around an iron core. The primary coils are connected to
the power supply while the secondary coils are connected to the
An electromagnetic field is created from the primary coils and this
induces a magnetic field in the core. This in turn induces a current in
the secondary coil.
The number of coils is proportional to the amount of voltage, so a
transformer is used to increase or decrease the voltage.
secondary voltage secondary turns
primary voltage = primary turns…read more
Electrostatic induction can be demonstrated
using small pieces of paper and a polythene rod.
The rod is negatively charged prior to the
experiment by vigorously rubbing it with a cloth.
It is then placed over the pieces of paper as
shown in the diagram
The pieces of paper jump up through the air to
the polythene rod and "stick" to it. This is
because when the negatively charged polythene
is brought close to the paper, the negative
electrons in the paper are repelled downwards.
The upper side of the paper becomes positively
charged and is therefore attracted towards the
negative rod. An everyday example of this is
when dust is attracted to a negatively charged TV
Things can also be charged by induction as
shown in the diagram
When the polythene rod is brought up close to
the cap of the electroscope, electrons are
repelled. If someone's finger is touching the cap,
the electrons will flow to earth via the person's
body. If the finger is then removed so that the
electrons cannot return, the rod can be taken
away and the electroscope will be left positively
charged. The gold leaf therefore rises because it
is repelled from the rod which has the same
charge as the leaf.…read more
Conductors / Insulators
Most materials fall into two groups: Conductors - allow electrons,
and therefore a current, to flow through them.
Insulators - do not conduct electricity
An insulator may act as a store of electricity known as static
electricity. There is a small third group called semi-conductors.
These partially conduct electricity but have different properties to
conductors. For example, as they are heated, their resistance goes
down. Conductors' resistance increase as they get hotter.
Current is carried by electrons. Metals contain a "sea" of free
electrons (negatively charged) which flow through the metal. This is
what allows electric current to flow so well in all metals.
Some important facts that you really should know:
Conventional current flows from Positive to Negative
Electrical current flows from Negative to Positive
So electrons flow opposite to the flow of conventional current…read more
Types of Circuit
Series Circuits Components are connected from end to end
Total resistance is the product of all the resistances added together
If one component is removed or disconnected the circuit is broken
Same current in all parts of the circuit
Total voltage of the supply is shared between components
The bigger the resistance of a component, the bigger its share of voltage
Parallel Circuits Each component separately connected
If one of the components is disconnected then it does not effect those it is
All components get the full source voltage (therefore the voltage is the same
in all the components)
The lower the resistance of a component the greater the current
Total current in the circuit is equal to the sum of the currents in its separate
Total current going into a junction is equal to the total current leaving it…read more