4.2.3.1 Direct and Alternating Potential Difference

Question 1

Direct current:

Answer 1

• the p.d. does not change polarity
• the electrons (current) flow(s) in one direction

Question 2

Common sources of direct p.d.:

Answer 2

• batteries
• cells
• solar cells

Question 3

Alternating current:

Answer 3

• the p.d. changes polarity
• the electrons (current) rapidly change(s) direction

Question 4

Sources of ac electricity:

Answer 4

ac generator

Question 5

What type of supply is mains electricity?

Answer 5

an ac supply

Question 6

What is the frequency and p.d. of domestic electricity supply in the UK

Answer 6

domestic electricity supply in the UK has a frequency of 50Hz (switches direction 50 times per second) and has a p.d. of about 230V

Question 7

How can scientists see the pattern of an electrical current?

Answer 7

using an oscilloscope

Question 8

Benefit of using alternating current:

Answer 8

very easy to use a transformer to increase or decrease the p.d. of ac (much harder to do this with ac)

Question 9

Alternating current on an oscilloscope:

Question 10

Direct current on an oscilloscope:

Answer 10

Question 11

How do you find the frequency of an alternating current using an oscilloscope?

Answer 11

• what would be the wavelength is the time period (T) - the time it takes for one complete cycle is the time period (T)
• frequency = 1/time period (f = 1/T)