Lesson test: Alternating current and its true value

1.[2p]
Alternating current is the form power is delivered in mainly because

transformers can step its voltage up and down efficiently, which needs a changing current

Correct

it is safer than direct current

The answer is: transformers can step its voltage up and down efficiently, which needs a changing current

it carries more charge

The answer is: transformers can step its voltage up and down efficiently, which needs a changing current

batteries produce it naturally

The answer is: transformers can step its voltage up and down efficiently, which needs a changing current

2.[2p]
The angular frequency of a 50 Hz supply is

about 314 radians per second

Correct

50 radians per second

The answer is: about 314 radians per second

100 radians per second

The answer is: about 314 radians per second

3140 radians per second

The answer is: about 314 radians per second

3.[2p]
The simple time-average of an alternating voltage is useless as its value because

it is positive as often as it is negative, so it averages to zero

Correct

it is always negative

The answer is: it is positive as often as it is negative, so it averages to zero

it changes too fast to average

The answer is: it is positive as often as it is negative, so it averages to zero

it equals the peak value

The answer is: it is positive as often as it is negative, so it averages to zero

4.[2p]
The RMS value of an alternating supply is defined as

the steady value that would dissipate the same average power in a resistor

Correct

the peak value of the wave

The answer is: the steady value that would dissipate the same average power in a resistor

the average of the voltage

The answer is: the steady value that would dissipate the same average power in a resistor

half the peak value

The answer is: the steady value that would dissipate the same average power in a resistor

5.[3p]
A mains supply is quoted as 120 V RMS. What is its peak voltage, in volts? Give it to the nearest volt.

CorrectNot quite: 170

6.[2p]
An alternating supply has a peak voltage of 12 V. What is its RMS value, in volts? Give two decimal places.

CorrectNot quite: 8.49

7.[2p]
Because the square of a sine wave is always positive, an alternating voltage delivers a real, non-zero average heating power even though its average voltage is zero.

True

Correct

False

The answer is: True

1.[2p] Alternating current is the form power is delivered in mainly because

2.[2p] The angular frequency of a 50 Hz supply is

3.[2p] The simple time-average of an alternating voltage is useless as its value because

4.[2p] The RMS value of an alternating supply is defined as

5.[3p] A mains supply is quoted as 120 V RMS. What is its peak voltage, in volts? Give it to the nearest volt.

6.[2p] An alternating supply has a peak voltage of 12 V. What is its RMS value, in volts? Give two decimal places.

7.[2p] Because the square of a sine wave is always positive, an alternating voltage delivers a real, non-zero average heating power even though its average voltage is zero.

1.[2p]
Alternating current is the form power is delivered in mainly because

2.[2p]
The angular frequency of a 50 Hz supply is

3.[2p]
The simple time-average of an alternating voltage is useless as its value because

4.[2p]
The RMS value of an alternating supply is defined as

5.[3p]
A mains supply is quoted as 120 V RMS. What is its peak voltage, in volts? Give it to the nearest volt.

6.[2p]
An alternating supply has a peak voltage of 12 V. What is its RMS value, in volts? Give two decimal places.

7.[2p]
Because the square of a sine wave is always positive, an alternating voltage delivers a real, non-zero average heating power even though its average voltage is zero.