Resistance

Question 1

What is resistance?

Answer 1

Resistance is a measure of how hard it is for a current to flow through a component in a circuit.

Question 2

Why are resistors used?

Answer 2

Resistors are added into a circuit to reduce the amount of current flowing.

Question 3

What happens if there is more resistance?

Answer 3

The bigger the value of resistance, the lower the current.

Question 4

What is a variable resistor or a rheostat?

Answer 4

A variable resistor or rheostat is a device with variable resistance. It can be used to vary the amount of current in a circuit.

Question 5

What is the equation for resistance?

Answer 5

resistance (Ω) = voltage (V) / current (A)

Question 6

What is the relationship between current and potential difference?

Answer 6

As the current changes in a component, so does the potential difference.

Question 7

What is the relationship between current and potential difference when there is a resistor?

Answer 7

The current flowing through a resistor at a constant temperature is directly proportional to the potential difference across it.

Question 8

What is the relationship between current and potential difference when there is a filament lamp?

Answer 8

Its resistance increases as the temperature of its filament increases. So the current flowing through a filament lamp is not directly proportional to the voltage across it.

Question 9

What is a filament lamp?

Answer 9

The filament lamp is a common type of light bulb. It contains a thin coil of wire called the filament. This heats up when an electric current passes through it and produces light as a result.

Question 10

What is the relationship between current and potential difference when there is a diode?

Answer 10

The diode has a very high resistance in one direction. This means that current can only flow in the other direction.

Question 11

What is a diode?

Answer 11

Diodes are electronic components that can be used to regulate the potential difference in circuits and to make logic gates. Light-emitting diodes (LEDs) give off light and are often used for indicator lights in electrical equipment such as computers and television sets.

Question 12

What are thermistors used for?

Answer 12

Thermistors are used as temperature sensors.

Question 13

What happens to thermistors at certain temperatures?

Answer 13

At low temperatures, the resistance of a thermistor is high and little current can flow through them.
At high temperatures, the resistance of a thermistor is low and more current can flow through them.

Question 14

What are LDR’s (light-dependent resistor) used for?

Answer 14

LDRs (light-dependent resistors) are used to detect light levels.

Question 15

What happens to LDR’s in certain light intensities?

Answer 15

In the dark and at low light levels, the resistance of an LDR is high and little current can flow through it.
In bright light, the resistance of an LDR is low and more current can flow through it.

Question 16

What happens when electric current flows through a resistor?

Answer 16

When electric current flows through a resistor some of the energy is transferred to heat energy.

Question 17

How does heat transfer take place? (using the example of metal)

Answer 17

Metals have loose electrons in the outer shells which form a ‘sea’ of delocalised negative charge around the close-packed positive ions. As the electrons move through the lattice structure of the metal they collide with ions in the lattice. Each of these collisions causes energy to transfer to the lattice in the form of heat. As a result, the metal heats up.

Question 18

What is the equation for charge?

Answer 18

Charge (coulomb, C) = current (ampere, A) × time (second, s)

Question 19

What is the equation for energy transferred?

Answer 19

Energy transferred (joule, J) = potential difference (volt, V) × charge (coulomb, C)