Andries 4 energy and change

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Information about Andries 4 energy and change

Published on September 6, 2013

Author: LKOTZE



Gr. 9 Natural Science South Africa NCS syllabus. Taken from Andries Olivier.

Energy and change

Mechanical systems to electrical

Van der graaff


Alternative sources

Electricity from nonrenewable sources


Electricity from renewable sources


Solar energy




Wave energy

Tidal energy

Nuclear energy


Store energy as chemical potential energy This is converted to electric energy when the battery/cell is connected to an appliance. R e m e m b cell battery

Inside the cell is a liquid called an electrolyte. Consist of millions of ions Two electrodes are suspended in the electrolyte. Two different electrodes cause a + pole and a – pole, just like a battery.

How does a battery work? Measured in volts Electricity will flow from the – to the + when a circuit is connected. The difference in charge is called potential difference

There must be a potential difference in an electric circuit for electricity to flow.

Wet and dry cells

The type of cell in the previous slides is a wet cell.

The type of cell in toys, radios and torches are called dry cells.

Flow of current as movement of charge.

Electric current is the movement of charge.

Direction (Conventional current)

The flow of positive charge from the positive pole of a cell to the negative pole of a cell through an external conductor.

Electric current is the opposite and flows from negative to positive.

We always use conventional current.

Coulomb (unit of charge)

Does your mum buy milk by the drop?

She buys it by the litre, because counting the drops will take forever!

In the same way, we count electrons in bundles. The unit of charge is thus a large amount of electrons together, called The coulomb. 1 coulomb = 6 250 000 000 000 000 000 = 6,25 x 1018 particles

The ammeter is used to measure how quickly charge flows past a fixed point in a conductor.

The ammeter is … Always connected in series in a circuit. Always connected positive to positive, and negative to negative.

Ampere (unit of current)

Q = It Charge in coulomb (C) Current in ampere (A) Time in seconds (s)

A coulomb is the amount of charge that flows past a certain point in a conductor in one second when the current that flows through it is one ampere.


Potential difference or electric charge - Ability of a cell to deliver electric current. Measured in volt (V)

The voltmeter is... always connected in parallel. connected positive to positive and negative to negative.



Things that allow current to flow through them are called conductors.

Things that don't allow the flow of current through them are called insulators.

Collisions between the charges and the particles of the conductor obstruct the flow of charge. This is called resistance.

Electrical resistance is the Obstruction a conductor offers against the flow of charge.

Ohm's law

Potential difference (V), in a simple electric circuit, is equal to the current strength (I) multiplied by the resistance (R).

V = IR Potential difference (V) Current in ampere (A) Resistance in ohm (Ω)

Potential difference (V), in a simple electric circuit, is equal to the current strength (I) multiplied by the resistance (R).

Factors that determine the resistance of a conductor Andries p 165

Factors that influence the resistance of a conductor: Type Length Thickness Temperature





Series circuit

Parallel circuit

If the potential difference increases, the current increases

If the resistance increases, the current strength decreases

Main current divides between parallel connected branches. Ammeter readings are the sameall over the circuit. Current in series and parallel

Potential difference is the sameeverywhere in a parallel connection. Potential difference dividesbetween the resistors. Pd in series and parallel

Increased amount of resistors = increased total resistance Increased amount of resistors = decreased total resistance Resistors in series and parallel

Increased total resistance Decreased total resistance Resistors in series and parallel

Current in each resistor is the same Current divides. Depends on the magnitude of the resistance Resistors in series and parallel

Vt = V1 + V2 Vt = V1 = V2 Resistors in series and parallel

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