Unit 1: Alternating Currents Flashcards
What happens in one cycle of an alternating current?
The charge carriers move one way in the circuit then reverse direction.
What is an alternating current?
A current that repeatedly reverses its direction.
What is the frequency?
The number of cycles the alternating current passes through each second.
What is the frequency for mains electricity?
50Hz
What is the equation for the time period?
1/f
What is the peak value of the alternating current?
The maximum current which is the same in either direction.
What does the peak current depend on?
The peak pd of the alternating current source and the components in the circuit.
What is the peak-to-peak value?
The difference between the peak value one way and peak value in the opposite direction - in other words twice the peak value
What does ‘sinusoidal’ mean?
The variation of an alternating current graph as it looks like a sine wave.
What does increasing the output pd from the signal generator lead to?
It makes the oscilloscope trace taller and this shows that the peak value of the alternating pd has been made larger.
What does increasing the frequency of the signal generator lead to?
It increases the number of cycles on the screen.
Why do our light bulbs not flicker?
The mains voltage is too high to see any flickering.
What are two equations for power?
P=IV and P=I squared x R
What is the equation for maximum power?
Peak current squared x R
What is the equation for the mean power?
0.5 x maximum power
What is the root mean square value of an alternating current?
The value of direct current that would give the same heating effect as the alternating current in the same resistor.
What is the equation for rms?
Peak/ square root of 2
How do we see a graph on an oscilloscope?
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.
What is the position of the spot of light on the screen affected by?
The pd across either pair of deflecting plates.
What causes the spot to deflect horizontally?
If a pd is applied across the x plates.
What causes the spot on the screen to deflect vertically?
A pd across the y plates.
What is the displacement of the spot proportional to?
The applied pd.
What are the x plates connected to?
The oscilloscope’s time base circuit.
What are the y plates connected to?
The y-input.
What is the calibration value for the y input referred to as?
The y sensitivity or the y gain.
How do you calculate the peak pd from an oscilloscope?
Volts per division x cm to peak (amplitude)
How do you measure the time period from an oscilloscope?
Time base x distance across screen horizontally between two places where pd is 0
What can be seen on an oscilloscope when a constant pd is applied to the y input?
A straight and horizontal line.
Why is the current that an oscilloscope draws from a circuit negligible?
It has a very high resistance.
How can you calculate the travel time of the pulse?
Distance horizontally to peak of pulse x time base
How can the speed of ultrasound be calculated?
Distance/travel time
