Resistance

Question 1

Define resistance

Answer 1

The resistance of a component is the ratio of current and voltage to the component

Question 2

State the equation for resistance

Answer 2

Resistance = voltage/current

Question 3

Define the Ohm

Answer 3

The Si unit of resistance, transmitting a current of one amp when subjected to a potential difference of one volt.

Question 4

State Ohm’s law

Answer 4

Ohm’s law states that the current through a conductor between two points is directly proportional to the potential difference across the two points

Question 5

Describe the benefits and uses of light emitting diodes (LED)

Answer 5

Although LEDs are more expensive to manufacture, they are more energy efficient therefore cheeper to run which eventually reduces the cost. They are beginning to replace bulbs in traffic lights for this reason, and are widely used to indicate when appliances are switched on.

Question 6

Describe the I-V characteristic for a filament lamp

Answer 6

The filament lamp is an ohmic device as when by the graph. The line passes through the origin and for low currents and voltages the line is relatively straight. With higher voltages the line begins to curve showing that the resistance has increased. Because a filament lamp’s temperature increases as a higher voltage is applied we can understand that the resistance is dependant on the temperature of the filament

Question 7

Describe the I-V characteristic for a LED

Answer 7

For positive voltages under 2V the current is almost zero, meaning the resistance is almost infinite. The LED will suddenly conduct at is threshold value, which is usually around 2V. The resistance for LEDs above 2V then drastically decreases. From this we can conclude LEDs are non ohmic devises as the resistance is dependant on the voltage of the LED rather than the temperature