Resistance

Question 1

What is resistance measured in?

Answer 1

Ohms

Question 2

What is the total resistance of a series circuit?

Answer 2

The sum of the resistances of the componants in the circuit.

Question 3

What does the resistance of thermistors depend on?

Answer 3

Temperature

Question 4

What does the resistance of a light dependant resistor depend on?

Answer 4

The light intensity.

Question 5

The resistance in a wire increases as:
-The length of the wire …..
The thickness of the wire …..

Answer 5

Increases, decreases

Question 6

What causes resistance?

Answer 6

An electric current flows when electrons move through a conductor, such as a metal wire. The moving electrons can collide with the ions in the metal. This makes it more difficult for the current to flow and causes resistance.

Question 7

The resistance of a … Wire is greater than the resistance of a …. Wire because electrons collide with ions more often.

Answer 7

Long, short

Question 8

The resistance of a .., wire is greater than the resistance of a … Wire because a …. Wire has fewer electrons to carry the current.

Answer 8

Thin, thick, thin

Question 9

R=v/I

3A flows through a 240V lamp. What is the resistance of the lamp?

Answer 9

R= 240/3 =80(ohms)

Question 10

A current flowing through a resistor at a constant temperature is directly ….. To the potential difference across it.

Answer 10

Proportional

Question 11

The resistance of a lamp increases as the temperature of its filament increases. The current flowing through a filament lamp is not directly propertional to the …. Across it.

Answer 11

Voltage

Question 12

What does a graph of a filament lamp look like?

Answer 12

A flat S

Question 13

An electric current flows when electrons move through a ….., such as a metal wire. The moving electrons can collide with the ions in the metal. This makes it more difficult for the current to flow and causes resistance. As the temperature increases, the metal ions vibrate more. There are more collisions with the electrons and so the resistance …..

Answer 13

Conductor, increases

Question 14

What are diodes?

Answer 14

Electric componants, which can be used to regulate the potential difference in circuits and to make logic gates.

Question 15

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

Answer 15

High

Question 16

What does the potential difference graph of a diode look like?

Answer 16

Straight line (at 0) and then a steep gradient upwards.

Question 17

A LED produces light when a current flows through it in the …… Direction.

Answer 17

Forward

Question 18

Thermistors are used as temperate sesnors. For example in fire alarms. Their resistance decreases as the temperate increases:

• at low temperatures, the resistance of a thermistor is …. And little current can flow through them.
• at high temperatures, the resistance of a thermistor is … And more current can flow through them.

Answer 18

High, low

Question 19

LDRS are used to detect light levels, for example in automatic security lights. Their resistance decreases as the light intensity increases:

• in the dark and at low light levels, the resistance of an LDR is …. And little current can flow through it.
• in bright light, the resistance of an LDR is …. And more current can flow through it.

Answer 19

High, low