Unit 2 - Electrical Circuits

Question 1

Describe how an ammeter and voltmeter should be arranged in an electrical circuit.

Answer 1

Ammeter in series ( in the same loop as the components)Voltmeter in parallel (across the component)

Question 2

What is the role of a variable resistor in a circuit?

Answer 2

It allows the current to be varied in the circuit.

Question 3

Three resistors in a series circuit have resistances 3, 5 and 2 ohms. What is the total resistance?

Answer 3

3+5+2 = 10 ohms

Question 4

The voltage of a battery in a parallel circuit is 3V. The circuit has 3 branches. How many volts does each branch get?

Answer 4

3V. Voltage is not shared in a parallel circuit. Each branch gets the full voltage of the battery.

Question 5

The voltage of a battery in a series circuit is 8V. There are only 2 resistors in the circuit both with the same resistance. What is the potential difference (voltage) across each resistor?

Answer 5

4V each. As the resistors are identical the energy is equally shared between them.

Question 6

Define current.

Answer 6

A flow of electrons.

Question 7

Define potential difference.

Answer 7

The energy transferred or work done per unit charge (just like the equation on your equation sheet says)

Question 8

Why does a bulb’s resistance increase as the energy is receives (potential difference across it) gets larger?

Answer 8

The bulb gets hotter.

Question 9

Give the unit for power.

Answer 9

W standing for Watts.

Question 10

What is a dc supply?

Answer 10

Creates a current flowing in one direction only. Batteries and solar cells produce dc supplies.

Question 11

What happens to the resistance of a bulb as it gets hot?

Answer 11

It increases. This is because the atoms in the wire of the bulb vibrate more so mobile electrons collide with the atoms more giving a greater resistance.

Question 12

What happens to the resistance of a thermistor when it gets hotter?

Answer 12

The resistance decreases as the heat energy is used to release more electrons to flow. The current increases.

Question 13

How does increasing the resistance in a circuit affect the current in the circuit?

Answer 13

As the resistance gets higher the current decreases.

Question 14

How does increasing the resistance of a resistor affect the potential difference across it if the current remains the same?

Answer 14

The potential difference increases. Current supplies more energy to get through the higher value resistor.

Question 15

The current beside the battery in a parallel circuit is 0.6A. The circuit has 3 identical branches. How much current flows through each branch?

Answer 15

The current splits evenly through each branch so 0.2 A each.

Question 16

What is an LED?

Answer 16

A light emitting diode. You must know the symbol, triangle, line, circle two arrows (light) moving away.

Question 17

Why is an LED more efficient than a filament bulb?

Answer 17

The LED wastes less energy as heat.

Question 18

What happens to a resistor when a current flows through it?

Answer 18

Electrical energy is transformed into heat energy.

Question 19

Give a use for a circuit containing a thermistor.

Answer 19

Anything that requires temperature to be monitored. A thermostat. A temperature sensor in a freezer/fridge/incubator etc.

Question 20

Give a use of a circuit containing an LDR?

Answer 20

A circuit that switches outside lights on when it gets dark.

Question 21

What does a diode?

Answer 21

A component which allows current to flow only in one direction as it has a huge resistance in the other direction.