A battery supplies energy to the rest of the circuit (chemical energy → electrical energy in the wires → light and heat energy in a lamp bulb). The potential difference can also be given in terms of these energy changes in fact the volt is equal to the joules of energy per coulomb.

So a battery supplying a potential difference of 4v gives 4 joules of energy to each coulomb of charge that passes through it.

Any electrical current provides a certain resistance to the flow of an electrical current. This can be thought of as the electrons having to push past the atoms in the conducting material. The higher the resistance the lower the current. Resistance is measured in Ohm’s by the Greek letter omega (Ω). Resistance in series can be added so 2Ω + 3Ω = 5Ω.

An equation for resistance is:

Potential difference across the wire (V)

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Current through the wire (I)

I got this equation as in 1826 George Ohm discovered that the current flowing through a metal wire is proportional to the potential difference across it. Providing the temperature remains constant.

Some factors that affect resistance are as the length increases, the resistance increases. As cross-sectional area increases, the resistance decreases. Copper is a good conductor and as temperature increases, the resistance of a wire increases.

Voltage graphs are different like the graph of an ohmic conductor is a straight line that passes through the origin; this shows that it obeys Ohm’s law. The graph of the filament lamp is a non-ohmic conductor as it is a curve and clearly does not obey Ohm’s law. As more current flows, the metal filament gets hotter and so its resistance increases this means the graph gets flatter. A thermistor is used in electronics and is made of a semi-conductor substance. As more current flows, the thermistor gets hotter and so its resistance decreases so the graph gets steeper.

Method – Connect a power supply to the resistor and an ammeter in series and connect a voltmeter. Measure the current at volt intervals of 0.5 up to 5 volts.

The test will be kept fair by making sure the temperature is kept constant, make sure that current is measured every 0.5 volts and other ways of keeping the test fair. Using the same apparatus E.g. Voltmeter and ammeter. Using the same wire as resistance is not the same in every wire. Letting the resistor cool before taking more readings as temperature can affect resistance.

The experiment will be kept safe by not going passed the full-scale deflection on meters. Not letting the resistor get too hot. Not using high voltages.

Results –

## Red Resistor Average = 2.26 (3s.f.)

## Blue Resistor Average = 6.40 (3s.f.)

Black Resistor – Average = 4.80 (3s.f.)

Conclusion – The graphs of all three resistors, blue, black and red obeyed ohm’s law as it went through the origin (0,0) meaning that ohm’s law was obeyed and that current and voltage were proportional at a constant temperature.

Current increases if voltage increases because current is the flow of electrons and voltage is the energy given to electrons so if you increase the voltage obviously, the current will increase as more power is given to the electrons. Yes the temperature is kept constant as the same wire is used. The blue resistor needs the most energy as it has the highest resistance.

The Filament lamp graph is a steep curved shape. It is this shape because the voltage increases as the current does not increase as much. The filament bulb has a high resistance so the electrons are stopped often and a lot of energy is released. This causes the filament to become hot and begins to glow, releasing light. The heat then causes the resistance to increase even more because the particles are vibrating faster and will stop the electrons more often. Therefore, a higher voltage is needed to allow the same current through or a lower current will pass at the same voltage.

The filament lamp does not obey ohm’s law, as the voltage across the bulb is not proportional to the current. This proves that ohm’s law is correct in saying voltage and current are proportional at a constant temperature as the filament bulb gets hotter and does not obey ohm’s law, therefore, it is not an ohmic conductor.