Unit 1: Alternating Currents

Question 0

What happens in one cycle of an alternating current?

Answer 0

The charge carriers move one way in the circuit then reverse direction.

Question 1

What is an alternating current?

Answer 1

A current that repeatedly reverses its direction.

Question 2

What is the frequency?

Answer 2

The number of cycles the alternating current passes through each second.

Question 3

What is the frequency for mains electricity?

Answer 3

50Hz

Question 4

What is the equation for the time period?

Answer 4

1/f

Question 5

What is the peak value of the alternating current?

Answer 5

The maximum current which is the same in either direction.

Question 6

What does the peak current depend on?

Answer 6

The peak pd of the alternating current source and the components in the circuit.

Question 7

What is the peak-to-peak value?

Answer 7

The difference between the peak value one way and peak value in the opposite direction - in other words twice the peak value

Question 8

What does ‘sinusoidal’ mean?

Answer 8

The variation of an alternating current graph as it looks like a sine wave.

Question 9

What does increasing the output pd from the signal generator lead to?

Answer 9

It makes the oscilloscope trace taller and this shows that the peak value of the alternating pd has been made larger.

Question 10

What does increasing the frequency of the signal generator lead to?

Answer 10

It increases the number of cycles on the screen.

Question 11

Why do our light bulbs not flicker?

Answer 11

The mains voltage is too high to see any flickering.

Question 12

What are two equations for power?

Answer 12

P=IV and P=I squared x R

Question 13

What is the equation for maximum power?

Answer 13

Peak current squared x R

Question 14

What is the equation for the mean power?

Answer 14

0.5 x maximum power

Question 15

What is the root mean square value of an alternating current?

Answer 15

The value of direct current that would give the same heating effect as the alternating current in the same resistor.

Question 16

What is the equation for rms?

Answer 16

Peak/ square root of 2

Question 17

How do we see a graph on an oscilloscope?

Answer 17

An electron gun at one end of the glass tube emits electrons in a beam towards a fluorescent screen at the other end of the tube, light is emitted from the spot where the beam hits the screen.

Question 18

What is the position of the spot of light on the screen affected by?

Answer 18

The pd across either pair of deflecting plates.

Question 19

What causes the spot to deflect horizontally?

Answer 19

If a pd is applied across the x plates.

Question 20

What causes the spot on the screen to deflect vertically?

Answer 20

A pd across the y plates.

Question 21

What is the displacement of the spot proportional to?

Answer 21

The applied pd.

Question 22

What are the x plates connected to?

Answer 22

The oscilloscope’s time base circuit.

Question 23

What are the y plates connected to?

Answer 23

The y-input.

Question 24

What is the calibration value for the y input referred to as?

Answer 24

The y sensitivity or the y gain.

Question 25

How do you calculate the peak pd from an oscilloscope?

Answer 25

Volts per division x cm to peak (amplitude)

Question 26

How do you measure the time period from an oscilloscope?

Answer 26

Time base x distance across screen horizontally between two places where pd is 0

Question 27

What can be seen on an oscilloscope when a constant pd is applied to the y input?

Answer 27

A straight and horizontal line.

Question 28

Why is the current that an oscilloscope draws from a circuit negligible?

Answer 28

It has a very high resistance.

Question 29

How can you calculate the travel time of the pulse?

Answer 29

Distance horizontally to peak of pulse x time base

Question 30

How can the speed of ultrasound be calculated?

Answer 30

Distance/travel time