P2 Revision Flashcards
What are components
A device in an electric circuit, such as a battery, switch or lamp
What is a fixed resistor
restricts or limits the flow of electrical current, the resistance does not change
Variable resistor
A resistor where the value of the resistance can be changed
Thermistor
An electrical device whose resistance decreases as its temperature increases- can be used in thermostats
Light dependent resistor (LDR)
A type of resistor which is affected by changes in light levels. Low light levels = high resistance, higher light intensity = resistance decreases
Name 2 types of current
- direct
- alternating
What happens in a direct current
The flow of electrons is in one direction only
What happens in alternating current
The direction of electron flow continually reverses
What is charge
A property of a body which experiences a force in an electric field (measured in coulombs)
What is the equation for charge
Charge = current x time
Q = I x t
Charge = coulombs
Current = amps
Time = seconds
What is current measured by
An ammeter
What does the current depend on
- the resistance of the component
- potential difference across the component
How do you measure potential difference across a component
A voltmeter must be placed in parallel with that component
- potential difference is known as voltage
What is the equation for potential difference
Potential difference = energy/charge
V = E/Q
What is the resistance over a longer piece of wire compared to a shorter piece of wire
The resistance is higher over a longer piece of wire. Resistance is directly proportional to length of wire
What is a diode
An electrical device that allows current to flow in one direction only
What is Ohm’s law
The rule that states that the current is directly proportional to the voltage across the resistor - provided that temperature remains constant
What is the series circuit?
A circuit, where one component follows directly from another.
Important key facts for series circuits
Current is the same through each component
The total potential difference of the power supply is shared between the components
The total resistance of the circuit is the sum of individual resistors
What does current do in a parallel circuit
The current will split
An ammeter can show/measure how the current splits
What happens to potential difference (voltage) in a parallel circuit
The potential differences is supplied equal across each of the parallel components
What happens when resistors are added to a parallel circuit?
The overall resistance is reduced as the current (electrons) may follow multiple paths
Why do wires heat up
Electrons flowing through wires, collide with ions Which causes the ions to vibrate more. increasing temperature.
Power and measurements
Power (watts) = current (amps) x potential difference (volts)
Power(watts) = current^2(amps)
x resistance (ohms)
What colour are the earth, neutral and live wire
Earth = green and yellow
Neutral = blue
Live = brown
What is the national grid
The network that connects all the power stations in the country to make sure that everywhere has access to electricity
What are transformers?
An electrical device that increases or decreases the potential difference (voltage) of an alternating current
Why do objects sometimes become electrically charged when rubbed against each other
Electrons which are negatively charge may be ‘rubbed off’ one material and onto the other. Leaves a positive and negative charge on the objects
Charges may attract or repel
How to draw an electric field
Arrow drawn from positive to negative charge
Closer together arrows are, stronger the force
