P5 Electricity and Magnetism Flashcards
What is an electric field?
A region of space in which the effects of
charge can be felt. When another charge
enters the field, both charges interact
and experience a force.
What is charging?
The addition or removal of electrons from
a material.
What is a conductor?
A conductor is a material which can
conduct electricity; electrons are able to
flow through it. copper, gold
What is an insulator?
An object which does not conduct
electricity. Electrons cannot flow through
the material.
How is static electricity produced?
When two insulators are rubbed
together, transferring electrons, to form a
positive and a negative charge.
What is an electric current?
Current is the rate of flow of charge in an
electric circuit.
What is required in order for a
charge/current to flow?
A potential difference
A closed circuit
Give an equation linking charge and
current, giving SI units
charge (C) = current (A) x time (s)
How is current measured
Using an ammeter, wired in series to the
circuit
What is conventional current?
Conventional current (used in circuit
diagrams etc.) represents the flow of
positive charge; it flows in the opposite
direction to the flow of electrons.
What is EMF?
Electromotive force (the voltage supplied
by a power source)
What are the units of EMF?
Volts, V
Define EMF in terms of energy
The energy supplied by the source per
unit charge around the circuit.
Define potential difference
The work done per unit charge flowing
between any two points.
How is potential difference measured?
Using a voltmeter, wired in parallel.
What is 1V equivalent to?
1 Joule per Coulomb
Give an equation linking current and
voltage, giving all SI units
p.d. (V) = current (A) x resistance (𝝮)
How does resistance affect the current
flowing through a circuit?
The larger the total resistance in the
circuit, the smaller the current will be.
How does resistance relate to the length
of a wire?
Resistance increases with length.
R ∝ L
How does resistance relate to the cross
sectional area of a wire?
Resistance decreases as cross sectional
area increases (they are inversely
proportional).
R ∝ 1/A
How is energy transferred in a circuit?
From the battery/power source to the
circuit components, and dissipated into
the surroundings as heat
What factors affect the energy
transferred when charge flows through a
component?
Amount of charge
● The potential difference across the
component
Resistance Formula is
R = V I.
What is a magnetic field?
A region where magnetic objects
experience a force.
Where is a magnetic field strongest?
At the poles of a magnet
Magnetic field strength decreases as…
Distance from the magnet increases.
Describe the key features of field lines in
a magnetic diagram
They have arrows pointing from north
to south.
● The lines never touch, cross or
overlap.
How is the strength of a magnet
displayed in a diagram?
By the spacing of the field lines (the
closer together they are, the stronger the
magnet)
What do the arrows on field lines
represent
The direction of the force that would be
experienced by the north pole of a
magnet placed in the field.
What is a permanent magnet?
An object which always has poles, and is
therefore always magnetic.
What is an induced magnet?
A magnetic material which does not have fixed
poles. They can be induced to become magnets
(giving them poles) by placing them in a
magnetic field, but they lose their magnetisation
when the field is removed.
What is a magnetic material?
A material that is attracted to a magnet
and can be magnetised.
Give examples of magnetic materials.
Iron, steel, cobalt, nickel etc.
Describe how materials are magnetised.
-Stroking them with a magnet
-Hammering them in a magnetic field
-Placing them in a coil with a direct
current through it
Describe how materials are demagnetised
-Hammering
● Heating
● Placing in a coil with an AC wire
What is a magnetically hard material?
A material which can be permanently
magnetised.
Give one example of a material that is
magnetically hard.
steel
What is a magnetically soft material?
A material which is only temporarily
magnetised (or does not hold its
magnetism very well)
Give an example of a magnetically soft
material.
Soft iron.
Give an example of where
electromagnets are more useful than
permanent magnets
Magnets used for moving scrap metal;
they can be turned off to drop the metal
where it needs to be transported to.
Describe how magnetic field shapes can
be investigated.
Using plotting compasses arranged
around a magnet; they will point towards
the north pole, showing the direction of
field lines.
