
Specific latent heat of fusion is defined as the amount of heat energy needed to change a
mass of 1 kg of a substance from a solid at its melting point into a liquid at the same
temperature.

Specific latent heat of vaporisation is the amount of heat energy required to change 1 kg of a
liquid at its boiling point into a vapour without a change in temperature.

NOTE THAT: The energy from heating is not being used to increase the speed of the
particles/increase the temperature but is being used to break the bonds between the
particles to change the state. A smaller number of bonds are broken during fusion than
vaporisation, this means more energy is required for vaporisation to occur.
1.9 Electromagnetism
A magnetic field is the area around an object where a magnetic force can be measured. The
direction of these field lines is always north to south
D.C motors
As a current flows through the coil of wire in the magnetic field, a force will act on the coil
causing it to move.
Eventually, the coil of wire will reach a state where the forces balance out and it stops
rotating, thus using the split ring ensures that the force on one side of the coil is always up
and the other side is always down.
As the coil turns, the split ring swaps contact with the brushes every half-turn (swapping the
+/-) keeping the rotation in the same direction. The direction of current must be swapped
every half turn, otherwise the movement will stop
The carbon brushes ensure that there is a connection between the power supply and the
split ring.
If a wire carries a current through a magnetic field, it will feel a force. The size of the force
depends on the following factors:
1. The size of the current. Increasing the current will increase the force on the wire.
2. The strength of the magnetic field. Using a stronger magnet will increase the force
on the wire.
3. The length of the wire in the field. Increasing the length of the wire will increase the
force. This is often done by creating multiple loops of wire.
Note: for a motor where motion is induced, the left hand is used; for a generator where a
current is induced, the right hand is used.
Electric Generators
 If a wire is moved through a magnetic field, it will cause a current to flow in the circuit. This
is known as electromagnetic induction. The direction of the movement is important: the
wire must cut the magnetic field lines. Therefore, no field lines are being cut and no
current will be induced.
 The size of the current induced can be increased by:
1.
2.
3.
4.
5.
increasing the strength of the magnetic field
increasing the speed of rotation
adding more turns to the coil
using a coil with a larger area
adding an iron core to the coil.
However, if the wire stops moving then no p.d is induced, this is due to the change
in the magnetic field that induces p.d . Further if the wire is connected in circuit,
then a current will be induced, because electrons will be able to move throughout
the circuit
A generator uses magnetic field and a moving wire to generate current in a circuit.
The movement of the wire, magnetic field and induced current all occur at right
angles to one another. Therefore, if the direction of the wire is reversed, the current
induced will be in the opposite direction
 Rotating the coil in a magnetic field induces an alternative current
 If the speed of rotation is doubled, the current produced will double but the current will
change direction twice as often. The frequency of the alternating current will also double as
shown in the graph below.
Transformers
An alternating current flow through the primary coil. This creates an alternating magnetic
field around the primary coil. The soft iron core becomes magnetised and strengthens this
magnetic field and connects the field to the secondary coil. Note that no current flows
through the iron core. The alternating magnetic field induces a voltage in the secondary coil.
This causes an alternating current to flow in the secondary coil. During use, the iron core
heats up. To reduce energy losses, a laminated (layered) iron core is used. This makes the
transformer more efficient.
1.7 Seismic Waves
In P – waves the paths are curved due to refraction as the waves travel further through each
layer. The properties of the rocks, such as density, change which causes changes in the
velocity of the wave. The sudden changes in direction at the boundaries between layers are
due to refraction at the boundary, as the rocks in one layer will have different properties to
the rocks in the next layer.
Note that the S - waves still follow a curved path due to refraction, but the S waves do not
cross the boundary between the mantle and the outer core. As S waves cannot pass through
liquids, it proves that the outer core must be a liquid.
1.3 Making use of energy
Conduction: is the primary mechanism of transferring energy in solid. When a solid is
heated, the particles in a solid vibrate more vigorously. For instance, when a metal rod is
heated, the particles near the heat source vibrate more vigorously and collide with nearby
particles, transferring some energy to those particles. This process repeats along the rod
until the heat has been transferred from the hot side to the cold side. Note that the bigger
the temperature (gradient) difference the greater the rate
of heat flow will be greater.
This process occurs in all solids, but metals conduct heat much better than non-metals. This
is due to free electrons in the metal. These move more quickly throughout the metal and will
cause the heat energy to be transferred from the hot side to the cold side more quickly.
Convection: is the primary mechanism of transferring energy in liquid and gas. When
heating, the particles in a gas or liquid gain energy and move more vigorously. This causes
the volume of the gas or liquid to increase and the density to decrease, as there are fewer
particles per cm3. The less dense gas will rise, and the colder, more dense gas or liquid will
sink to take its place. This process will continue until all of the gas or liquid particles are
heated.
The main methods of insulating the home include:
1.
2.
3.
4.
loft insulation
double glazing
cavity wall insulation
draught excluders.
1. Loft insulation: Loft insulation involves laying fibreglass wool on the floor of the attic. This
wool is a good insulator because it contains lots of pockets of air. This reduces conduction
through the ceiling into the loft space so the rooms below the ceiling remain warmer for
longer. The temperature just above the loft insulation is lowered, so there is less convection
of air within the roof space.
2. Double glazed windows have two panes of glass separated by a gap filled with air. The air is
a good insulator, which reduces conduction through the window.
3. Cavity wall insulation will fill the gap between two layers of bricks with foam or fibreglass
wool. This wool will trap lots of pockets of air. As the air is a good insulator, this reduces
conduction through the wall. The wool will also reduce convection currents within the cavity
as the air will not be able to move. Sometimes a space is left between the fibreglass and
outer wall. The fibreglass still acts as a good insulator and reduces convection, since the air
space is smaller. Often, the fibreglass wool panels will have a shiny silver foil coating. The
inner shiny surface will reflect thermal radiation back into the house. As shiny silver surfaces
are poor emitters, this will reduce heat losses due to radiation. Consequently, the
temperature of the outer wall is less, reducing convection losses from the outside wall.
4. Draught excluders fill gaps around doors and windows to reduce convection currents by
reducing the movement of air into and out of the house.
Effective house insulation will reduce the energy consumption of a house. Less heat is lost
per second; therefore, less heat energy will be required per second to maintain the same
temperature in the house. This means that the energy bills will be lower. As the energy
consumption will be reduced, less fossil fuels will be required to produce the heat energy.
This means less carbon dioxide will be produced, reducing the impact on global warming.
1.2
The National Grid consists of a network of power stations, transformers and power lines all
joined together supplying electricity to consumers. Supply and demand are monitored. At
times of power station failure electricity can be transferred from one part of the Grid to
another. At times of peak demand, reserve generation can increase supply or electricity can
be imported from abroad. Transformers are used to step-up the voltage before transmission
along power lines. This reduces current and power loss as heat in the cables.
1.5 Waves
Waves are faster in deep water. However, when wave passes from deep to shallow water
the frequency remains constant