Topic 10 Flashcards
What is current ?
Electrical current is the flow (movement) of electric charges
What is electrical current measured in ?
Electric current is measured in amperes (A). Current has the same value at any point in a single closed loop
How do you calculate the flow of charge ?
The flow of charge (C) = current (A) x time (s).
In a closed loop if the current is 10(A) in one point what is it at another point?
10(A)
Because A current has the same value at every point in a single closed loop.
I = Q/t
Current (C) = charge(A) / time (s)
Coulombs Amps Seconds
current = charge / time
How would you rearrange this equation if you wanted to calculate charge ?
Charge = current x time
What are the units for current?
Amperes
What is an electrical conductor ?
An electrical conductor is material that allows electric currents (flow of electric charges) to pass through it.
What are all electrical conductors made from ?
All metals are electrical conductors
What are electrical insulators ?
An electrical insulator is a material that doesn’t allow electric currents (flow of electric charges) to pass through it.
What are two electrical insulators ?
Plastic and glass are electrical insulators
What allow electrical conductors too conduct electricity?
The free electrons inside electrical conductors explain why they can conduct electricity
What makes an electrical insulator ?
An electrical insulator has no free electrons.
No charges are free to move and carry a current.
What makes an electrical conductor ?
An electrical conductor has lots of charges that are free to move.
In a metal, the charges that are free to move are electrons.
The electric current through the metal is the flow of these free electrons
What is potential difference ?
Potential difference is the difference in the amount of energy that charge carriers have between two points in a circuit.
How can potential difference be described ?
It can be described as the energy transferred by unit charge passed
What is potential difference measured in ?
Potential difference (p.d.) is measured in volts (V) and is also called voltage. The energy is transferred to the electrical components in a circuit when the charge carriers pass through them.
What do we use to measure potential difference ?
We use a voltmeter to measure potential difference (or voltage).
V =?
E / Q
Voltage x charge = ?
Voltage x charge = energy
What do ammeters measure ?
An ammeter measures the flow of current that passes through a wire
How do ammeters have to be connected ?
Ammeters have to be connected in series (in the same loop of the circuit) with the electrical component whose current you are measuring.
What do voltmeters measure ?
Voltmeters measure potential difference (voltage) between two points in a circuit.
For example between two points either side of a component.
How do voltmeters have to be connected ?
Voltmeters must always be connected in parallel (on a separate branch of the circuit) with the two points being measured.
What’s the difference between current and potential difference ?
The current is a flow of charge. Current is measured through a component.
Potential difference is the energy used between two points in a circuit, therefore it is measured between two points either side of a component.
We describe this as the potential difference measured across a component.
If voltage is 5V and charge is 3C, what is the energy transferred?
Voltage = energy / charge
Energy = voltage x charge
5V x 3C = 15J
Fact
A potential difference of one Volt is equal to one Joule of energy being used by one Coulomb of charge when it flows between two points in a circuit
What is resistance a measure of ?
Resistance is a measure of how difficult it is for current to flow through a component
How is resistance measured ?
Resistance is measured in ohms, Ω.
When charge flow is in an electrical current the size of the current is affected by what two things?
The resistance: If the resistance is increased, the current will decrease.
The potential difference: If the potential difference is increased the current will increase.
What is ohm’s law ?
The resistance between two points in a circuit is equal to the potential difference between those two points, divided by the current flowing through them.
What’s the symbol and word equation for ohms law ?
R = V/I Resistance = potential difference/current
How would Ohm’s Law be rearranged to calculate potential difference .
Potential difference = current x resistance
What instruments do we use to calculate resistance ?
We calculate potential difference using a voltmeter and current using an ammeter at the same time
When a wire is longer what does this do to the resistance?
The longer the wire, the higher the resistance
What do we use to measure a current flowing through a component ?
Ammeter
To measure the resistance of a component (e.g. lamp or resistor) what should we do ?
measure the potential difference across the component.
What is An Ohmic conductor ?
a conductor that obeys Ohm’s Law.
If The current through an ohmic conductor (at a constant temperature) is directly proportional to the potential difference across the resistor. What does this mean for the resistance?
This means that the resistance remains constant as the current changes.
To measure resistance what do you need ?
A voltmeter in parallel
An ammeter in series
Ohms law
