Magnetism and Electricity, Grade 10 Electricity and Magnetism, IGCSE Physics: Electricity & Magnetism

Complete the sentence. "The greater the resistance across a component..."

"...the smaller the current that flows."

Why are Ammeters and Voltmeters an exception in PARALLEL and SERIES CIRCUITS?

- Ammeters are always connected in series, even in a parallel circuit - Voltmeters are always connected in parallel with a component, even in a series circuit

What are basic factors of a SERIES CIRCUIT?

- Components connected in a line, end to end - If one component is removed the circuit brakes and all will stop.

Explain the basic factors of PARALLEL CIRCUITS

- Each component is separately connected to the positive and negative of each supply - If one component is removed, it will hardly affect the rest - Used most commonly in real life, e.g. cars and houses

When can LDRs be used?

- Outside night lights - Burglar detectors

What are the uses of Thermistors?

- Temperature detectors - Car engines - Thermostats

In an electric circuit...

...it is more usual to measure the current through the appliance and the potential difference across it rather than the energy transferred and the time. So we can use current and potential difference to calculate the power of the appliance using the equation: P = I x V

series circuit

A circuit with only one path for an electric current to flow.

parallel circuit

A circuit with two or more conducting paths between any two points in the circuit.

What is a Current and what is it measured in?

A current is the flow of electric charge round the circuit. Current will only flow through a component if there is a potential difference across that component. It is measured in AMPERES (A)

alternating current

A current that continually changes direction.

Positive

A material has this charge when it loses electrons.

resistance

A measure of how difficult it is for current to pass through a part of a circuit. Measured in ohms.

efficiency

A measure of how effectively energy is transformed into a useful form.

voltage

A measure of the energy converted per unit charge passing through a component. also a measure of the amount of energy transferred to electrical form per unit by an electrical power supply, like a battery.

voltmeter

A measuring instrument for measuring the voltage between two points in a circuit.

Explain potential difference in a PARALLEL CIRCUIT

All components get the full source of potential difference so the voltage is the SAME across all components

A.C.

Alternating Current - a value in which the current (and potential difference) oscillates between two values, one of which is positive and the other negative.

Electrical power and potential difference

An electrical appliance transfers electrical energy into other forms of energy. The rate at which it does this is called the power. Power can be calculated using the equation: P = E/t.

ammeter

An instrument used to measure the size of current in a circuit.

Why don't appliances with plastic cases need to be earthed?

Appliances with plastic cases do not need to be earthed. They are said to be double insulated and are connected to the supply with two-core cable containing just a live wire and a neutral wire.

Direct current

Causes electricity to flow in one direction only.

Alternating current

Causes the current to change continuously, with electricity flowing in one direction then the other.

D.C.

Direct Current - a value in which the current (and potential difference) is a constant amount.

transformers

Electromagnetic devices used to increase or decrease the size of alternating voltage electricity supplies.

free electrons

Electrons which are not bound to any particular atom in a solid. These are free to move and enable charge to move through a material forming an electric current.

electron

Extremely small particle carrying negative charge and making up the outer 'shell' or 'shells' of an atom.

earthed

Having a very low resistance connection to the general mass of the earth, taken as always being a 0 V.

neutral

Having no overall electric charge. Neutrons are electrically neutral because there is a balance between the number of negative charges on electrons and the number of positive charges on the protons which make up part of the nucleus.

What do LDRs do?

Light Dependant Resistors are dependant on the intensity of light. Their resistance falls in bright light and rises in darkness.

Atom

Made up of neutrons and protons which make the nucleus, which is surrounded by fast moving electrons.

conductors (electrical)

Materials that allow electricity to pass through them easily. Most metals are good electrical conductors.

soft magnetic materials

Materials that are easy to magnetize and demagnetize.

Conductors

Materials that conduct electricity well. They are usually metallic.

Insulators

Materials that do not conduct electricity at all. They are usually non-metallic; rubber, glass and many types of plastic.

hard magnetic materials

Materials that retain their magnetism well.

What happens when certain insulating materials are rubbed together?

Negatively charged electrons will be scraped off of one and transferred on the other leaving a positive static charge on one and a negative static charge left on the other.

Electrons

Negatively charged particles which surround the nucleus of an atom.

Neutron

Neutral particles in the nucleus of an atom.

P = E/t

P is the power in watts, W E is the energy transferred in joules, J t is the time in seconds, s.

Proton

Positively charged particles in the nucleus of an atom.

magnetic

Possessing the ability to attract iron and its compounds.

Explain Potential Difference in a SERIES CIRCUIT?

Potential Difference is SHARED between the various components so the voltages round a series always add up to equal the source voltage.

What is Potential Difference and what is it measured in?

Potential Difference is the driving force that pushes the current round. It is measured in VOLTS (V)

Equation which links Resistance, Current and Potential Difference

Resistance = Potential difference / currents

What is Resistance and what is it measured in?

Resistance is anything in the circuit which slows the flow down. It is measured in OHMS (Ω)

amp

The SI unit of electric current.

Voltage

The amount of energy is transferred per coulomb of charge that is passed through the battery. Measured in volts.

electric charge

The property of particles that causes electric effects.

Power

The rate at which electrical energy is converted in an appliance. Measured in watts.

Current

The rate of flow of electric charge through a conductor. Measured in amps.

current

The rate of flow of electric charge.

power

The rate of transfer or conversion of energy.

Ohm's Law

The resistance of a circuit component is constant unless outside conditions (specifically temperature) are changed.

Explain Current in a SERIES CIRCUIT

The same current flows through all parts of the circuit so it is the same everywhere. The size of the current is determined by the total Potential Difference of the cells and the total Resistance of the circuit

Explain current in a PARALLEL CIRCUIT

The total current flowing around the circuit is equal to the total of all currents through the separate components. There are junctions where the current either splits or rejoins. The total current going into the junction has to equal the total current leaving. If two identical components are connected in parallel the same current will flow through each component.

Explain Resistance in a SERIES CIRCUIT

The total resistance is just the sum of all the resistances. The bigger the resistance of a component, the bigger its share of the total potential difference

Series Circuit (Kirchoff's law)

The total resistance is the sum of each component in the circuit. Total resistance = r1 + r2 so the current is the same at every point in the circuit.

negative electric charge

The type of charge possessed by the electron.

positive electric charge

The type of charge possessed by the proton.

watt

The unit of power equal to a rate of transfer of energy of 1 joule per second.

volt

The unit of voltage. 1 volt is equal to 1 joule of energy per coulomb of charge passed through a component.

Parallel Circuit (Kirchoff's law)

The voltage is the same across each branch. V(total) = v1 = v2 The total current through the circuit is the sum of the current through each component. I(total) = i1 + i2

Explain Cell Voltages in a SERIES CIRCUIT

There is a bigger potential difference when more cells are in series, provided the cells are all connected in the same way. For example, when 2 batteries of voltage 1.5V are connected in series they supply 3V between them

What do Thermistors do?

They are temperature dependant resistors. Their resistance decreases in hot conditions and increases in cool conditions

ohm (Ω)

Unit of resistance; the resistance of a conductor that passes a current of 1 amp when a voltage of 1 volt is applied across it.

Ohm's Law Formulae

V = I x R

Explain how RESISTANCE increases with TEMPERATURE

When charge flows through a resistor, some of the electrical energy is transferred to heat energy and the resistor gets hot causing the ions in the conductor to vibrate more making it more difficult for the charge to carry electrons to get through the resistor - the current can't flow as easy and the resistance increases.

P = I x V

Where: P is the power in watts, W I is the current in amps, A V is potential difference in volts, V

open circuit

a circuit that is not connected in some area, so elements of electrons do not flow

gravity

a foce that pulls all objects and materials to Earth

temporary magnet

a magnet with a force field that attracts other objects for a short period of time

permanent magnet

a magnet with a force field that will remain all the time

conductor

a material that allows electricity to easily flow through it (metals, water, and people)pa

insulator

a material that blocks the flow of electricity through it (rubber, plastic, and glass)

compass

a tool that uses a magnet to point in the direction of the Earth's magnetic poles

magnetic field

an area of magnetic fore surrounding a magnetc

closed circuit

complete circuit that allows the flow of electrons to flow through completely

electromagnet

created by an electric current running through a coil

series circuit

electricity flows in one path or in a single loop If any bulbs burn out, the others will go out too.

parallel circuit

electricity flows in two or more paths or loops If there is a break in the loop, the other bulbs will still light.

iron, cobalt, nickel, steel

metals that are magnetic

resistor

modifies current and voltage

static electricity

occurs when there is an imbalance of positive and negative charges (does not flow)

magnet

something made of iron or steel that is attracted to substances made of a magnetic material

poles

the two ends of any magnet

repel

what happens when pole push away from each other

attract

what happens when unlike poles pull together

magnetic

when an object attracts or repels a magnet

current electricity

when electrons flow through a circuit items are connected to a power source (battery or plug)