P5 Flashcards
What is an atom made up of?
charged particles.
What are between charged objects?
electrostatic forces.
What is an example of electrostatic forces?
hair standing up when it attached to a charged comb.
The outermost electrons are less…
strongly attracted to the nucleus.
What does a variable resistor do?
A device that allows you to control the current by changig the resistance wire.
Resistance=
Voltage (in volt)s / current (in Amps)
What is a series circuit?
When the components are connected in a line.
In a series circuit, the current is..
The same through all the components.
How can the outermost electrons in static electricity be removed?
By rubbing
What happens when two insulating objects are rubbed together? Why?
They become charged. This is because electrons are transferred from one object to the other.
What happens when you brush your hair?
Individual hairs become similarly charged and repel each other, making your hair stick up.
What happens when you take off a nylon or polyester top?
Electrons move through the air from the negatively charged clothing to your positively charged hair.
What builds up during a thunderstorm? What is the effect of this?
Charge, which flows between the cloud and the Earth as a flash of lightning.
Why are metals good conductors of electricity?
Because they have free electrons, which means there are lots of charges free to move.
Why are plastics electrical insulators?
Because there are few free electrons in the plastics, which means there are few charges free to move.
When the bulb is lit in a circuit…
there is an electric current.
In a complete circuit…
there are free electrons in all the metal components and connecting wires.
The flow of charge is the…
electric current.
What is electric current?
the rate of flow of charge.
What is electric current measured in?
Amperes.
The more energy the charged particles receive from the power supply..
the greater the current.
In an electric current..
charge is conserved and energy is transferred.
What is used to measure current?
An ammeter.
What is the unit for voltage?
volt.
The larger the voltage of the battery in a circuit…
the bigger the current.
What is voltage?
The measure of how much energy is supplied to the circuit and how much energy is transferred in the component.
Power=
voltage x current
What does a voltmeter measure?
the difference in energy between the terminals of a battery and a bulb.
What is potential difference (p.d)?
The difference in energy per unit.
The more resistance in a circuit…
the lower the current.
The greater the voltage across a resistor..
the larger the current.
What is resistance?
a measure of how much a conductor opposes the current.
What is a variable resistor?
a device that allows you to control the current by changing the amount of resistance in a circuit.
Resistance=
Voltage (in volts) / Current (in amps).
A graph of voltage against current will give you…
a straight line through the origin.
The higher the resistance in a graph…
the lower the gradient.
In a series circuit, is the current the same or different through all the components connected?
The same
The more cells connected in a series…
the greater the potential difference.
The p.d across the components in a series circuit will be proportional to..
its resistance.
What is a thermistor?
A semi conductor whose resistance changes with temperature.
What is a light dependent resistor?
A semiconductor whose resistance changes as the amount of light falling on i changes. In bright light, the resistance will be low.
What is a magnetic field?
a space around a magnet in which a magnetic force acts.
Where is the magnetic field strongest?
Where the field lines are closest together.
When is a voltage induced?
When a magnet is moved near a piece of wire.
When is a current ALWAYS induced?
When there is relative movement between the magnet and the coil of wire.
When is the direction of current reversed?
When the motion of the wire is reversed, so the magnet turns around.
When will current increase?
- a stronger magnetic is used
- the speed of motion increases
- there are more turns of wire in the coil
When is there a continuous supply of electricity produced?
When there is a continuous relative motion between the magnet and a coil of wire.
When is a larger voltage induced?
- the strength of the magnet is increased.
- the number of turns in the coil is increased.
- the rate at which the coil is turned increased.
- an iron core is used inside the coil.
The faster the rate of cutting field lines…
the larger the induced voltage.
How is mains electricity produced?
By generators in power stations that induce an alternating voltage.
As a coil rotates in a uniform magnetic field..
…it cuts the lines of magnetic field at different rates.
When the coil is at a right angle to the field lines…
…it cuts no field lines so the induced voltage is zero.
When the coil is parallel to the field lines…
…its rate of cutting field lines is at a maximum, so the inducted voltage is at a peak.
As the coil rotates…
it cuts field lines in a different direction, so the direction of the voltage alternates.
What is direct current (d.c.)?
Current that always flows in the same direction. E.g. batteries.
What is alternating current (a.c.)?
Current that changes direction at regular intervals.
What are transformers used for?
to step up the voltage at the power station and to step down the voltage near near our homes.
Why is the UK’s electricity supply a.c?
Because it is easier to generate a.c current in large amounts.
