Heat

Heat is a form of energy

• Heat is measured in Joules (J).
• Heat always flows from hot to cold objects.
• Temperature is a measure of how hot or cold something is
• temperature can be measured in degrees Celsius (^ºC).

• The faster the atom is moving the hotter the object is
• In a solid the atoms vibrate on the spot
• In liquids and gasses they also are moving around at all times.

Heat can move by conduction, convection or radiation.

• The Celsius scale was worked out using water
• The boiling point of pure water is 100 ºC
• The freezing point of pure water is 0 ºC

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Conduction of Heat.

Heat moves best through solids by conduction

• Metals tend tbe good conductors of heat
  • E.g. copper, aluminium, brass and steel
• Non-metals tend tbe poor conductors of heat
  • E.g. glass, plastic, ceramic and wood
• When an atom of metal is heated it vibrates faster
  • It quickly passes its vibrations on to its neighbouring atoms
  • In this way the heat is quickly conducted through the solid

Convection of Heat.

Heat can move best through fluids by convection.

• A fluid is something that flows like a liquid or gas
• heat rises in a fluid during convection

As the atoms and molecules of the fluid are heated they move faster.

• When they move faster they need more space.
• The hot fluid is lighter than the cooler liquid
• The hot fluid floats up through the cooler

Conducted heat rises

Radiation of Heat.

Radiation is another method by which heat travels through liquids and gases

• Radiated heat travels in all directions away from the hot object
• Radiation is the only type of heat movement that does not need particles.
• Radiation is the only way that heat can travel through the vacuum of space from the sun to the earth.

Electricity.

Electricity is a form of energy.

A circuit is a number of electrical components (parts) connected together.

The symbols for the components of a circuit are:

;
;	Battery	length of wire	switch	bulb	motor

Series and Parallel circuits.

• A series circuit connects components in a row.

• the current is the same at all points in a series circuit.
• A parallel circuit connects components side by side.

the current is split between the components in a parallel circuit

Measuring Electricity.

Current

• An ammeter is a component that measures electrical current

• Current is a measure of how much electricity is flowing in a circuit

• An ammeter is connected in series with the other components
• Current is measured in amps.

Voltage

• A voltmeter is a component that measures the voltage across a component

• A voltmeter is connected in parallel with the other components

• The voltage across a component is a measure of how much electrical energy it uses
• Voltage is measured in volts
• Components will always have a voltage rating at which they should be operated
• Too much voltage an the component will be damaged
• Too little voltage and it will work badly or not at all

Resistance in a circuit.

Materials/components have a property called electrical resistance.

• The symbol for a resistor is:

• The higher the electrical resistance of a component the less current flows through it.
• As you move the ammeter from right tleft the current drops

• A current flowing through a wire creates a magnetic field.

• An electromagnet is made of wire coiled round an iron or steel core with a current flowing through the wire
• Electromagnets are used for:
  • electric bells
  • cranes for lifting metal in steel works and construction sites

A relay is a method of turning large amounts of electricity on and off using a small amount

• When the small voltage is off the magnet is off
  • The spring holds the switch away from the contact
  • The larger current cannot flow.
• When the small voltage is on the magnet is on
  • The magnet pulls the switch tthe contact
  • The larger current flows.
• Relays are used in:
  • car electrics
  • and many other electrical applications where a large voltage has tbe switched

Vocabulary