Current

Question 1

Define the Ampere.

Answer 1

1 Ampere is 6.25x10^18 electrons passing a point every second.

(i.e. 1 A = 1 C/s)

Question 2

What does Joule’s law state?

Answer 2

That the rate of heat produced is proportional to the square of the current (when resistance is constant).

Question 3

What is electric current?

Answer 3

The flow of electrons.

Question 4

Give a property of direct current.

Answer 4

It flows in ONE direction only.

Produced by cells and batteries

Question 5

How does current flow according to conventional current?

How does current flow in reality?

Answer 5

• Conventional: Current flows from positive to negative.

- Reality: Current flows from negative to positive.

Question 6

Give the formula for charge (in terms of current and time).

Answer 6

Q = I x t

Question 7

Where is an ammeter placed in a circuit when measuring current?

Answer 7

In series. This is because current is constant throughout a series circuit.

Question 8

What are the effects of current?

Answer 8

• Magnetic effect
• Heating effect
• Chemical effect

Question 9

What is the significance of the heating effect of current?

Answer 9

• Massive amounts of heat can be lost through energy transfer across long distances.
• Electrical equipment can overheat/melt.
• Current can be used for heating objects via heating elements.

Question 10

How do you demonstrate the magnetic effect of current?

Answer 10

• Place a compass on a wire.
• Switch on the circuit, the compass needle deflects.
• Switch off, returns to normal.

Question 11

How do you demonstrate the chemical effect of current?

Answer 11

• Connect an anode (copper) and a cathode (zinc) plate to a power supply and run a current through the circuit.
• The copper anode dissolves and the iron cathode is coated in the copper ions.
• This is called ‘electroplating’.

Question 12

How do you demonstrate the heating effect of current?

Answer 12

• Connect an insulated calorimeter to a power supply.
• Let a current flow through the circuit and measure the temperature over a set time with a digital thermometer.
• The current value will be proportional to the kelvin temperature.