Alternating currents

Question 1

AC graph

Answer 1

sinusodial curve

Question 2

Period

Answer 2

Time taken for one complete cycle of AC

Question 3

Peak value

Answer 3

Amplitude of the oscillating current or voltage

Question 4

Root mean square value of an alternating current is?

2 marks

Answer 4

that steady current which delivers the same average power as the ac to a resistive load

Question 5

Half-wave rectification

Answer 5

Diode allows current to flow in 1D only so output will only consist of positive half-cycles. Diode rejects negative outputs

Question 6

Smoothing

Answer 6

Capacitor charges up to the rising part of the half- cycle and then discharges through the resistor as Vout falls. This reduces fluctuations

Question 7

large capacitor affects smoothing how

Answer 7

discharges slowly so will give a small ripple

Question 8

high resistance affects smoothing how

Answer 8

slower discharge of capacitor so smaller ripples

Question 9

How to find if a capacitor is suitable for smoothing

3 points

Answer 9

• calculate RC, time constant of capacitor
• compare with the time interval berween adjacent peaks
• time constant closer to the interval is more suitable as it will discharge between peaks

Question 10

by making reference to the heating effect

what is the rms value of an alternating current

Answer 10

the steady current that produces the same heating effect as the ac

Question 11

how to calculate rms

Answer 11

Peak value/ √ 2

Question 12

Power formula

Answer 12

Vrms²/ R

Question 13

Advantage of using ac rather than dc

Answer 13

easy to change voltage

Question 14

Disadvantage of using ac rather than dc

2

Answer 14

• cables require greater insulation
• rectification- have to create a bridge rectifier