Resistance and Power

Some components are made of materials which electrons have difficulty travelling through. This property is called…

resistance.

When the resistance in a circuit increases,

the number of electrons flowing through the circuit decreases.

Many components in an electrical circuit have resistance. This means that…

the electrons must use up some of their energy (voltage) in overcoming resistance. This energy is transformed into other useful forms, such as heat, light, and sound.

Circuits sometimes have special components called resistors which limit…

the flow of electrons in a certain branch of the circuit.

What reduce the damage that could occur to the components should the current be too high and cause the components to overheat?

Resistors

Some resistors have a fixed resistance rating, however,…

there also those for which their resistance can be altered. These are called variable resistors or rheostats.

Variable resistors…

are those for which their resistance can be altered. Variable resistors have a slide on top which moves to alter the amount of current that can flow through it.

Potentiometer

A potentiometer is another form of variable resistor which has a knob which can be turned to adjust the current flow. These are often used in audio equipment to adjust the sound output

Resistance is measured in units called…

ohms (which has the Greek letter Omega () as its symbol). One ohm is equal to a voltage loss of 1 volt for every amp of current.

Describe how the voltmeter and ammeter are positioned in the circuit in relation to the lightbulb.

Voltmeters are always connected in parallel “piggybacking” the component Ammeters are connected in series inside the circuit.

Relating Voltage, Current and Resistance – Ohm’s Law

The amount of current passing through a component such as a lightbulb increases, the amount of voltage lost across that component also increases i.e., current is proportional to voltage loss.

For the slope of the graph to remain a straight line, the temperature of the component must remain constant. This is known as…

Ohm’s law.

All components within a circuit transform electrical energy into…

some other useful form of energy.

Lightbulbs transform electrical energy into light, resistors turn electrical energy into heat and motors turn electrical energy into kinetic energy.

The power rating or wattage of a component…

determines whether a component transforms this energy slowly or rapidly.

Components which slowly transform electrical energy into another form will have…

a low power rating, while those with a higher power rating complete their energy transformations much faster.

The concept of power, can also be applied to…

electrical energy and circuits.

Power (P) is defined as:

The rate at which energy is supplied or used by a component and has the symbol Watts (W).

1W of power =

1J of energy per second

Power is proportional to…

both voltage and current.

This means that if more voltage or current is supplied to a component then it will receive more energy and consequently have more power

The power for a component in an electrical circuit can therefore be found using the equation:

P = V x I

To find the total energy (E) produced or used by a component, we can use the equation:

E = P x t