Electricity Flashcards
What is alternating current?
An alternating current (a.c.) changes its direction and instantaneous value with time.
What is direct current?
In direct current (d.c.), the electrons flows in one direction only. Its value is constant.
In an oscilloscope what does the “time base” control?
time base” controls how much time each division on the x-axis is worth.
In an oscilloscope what does the “Y- Gain” control?
“Y Gain” controls the voltage each ‘division’ on the yaxis is worth.
What does the a.c current trace look like?
What does A.C look like on an Ossocilsope?
What does D.C look like on an Ossocilsope?
Solid line———————————
How do you calculate the peak voltage?
Peak voltage = Number of divisions x volts per division
Number of divisions x time per division = what
PERIOD (T) of the wave (length of one wavelength across)
What is the equation for frequency?
frequency (f) = 1/T
What happens when the timebase of the ossolociope is turned off?
The a.c. the signal will not spread along the xaxis. The voltage variation will continue to oscillate up and down meaning a straight vertical line will be displayed on the screen.
Aa.c. voltages are stated in terms of their r.m.s. (root mean square) values what are R.M S Values?
These are a kind of ‘average’ of the alternating a.c. supply.
Where is the peak voltage of the wave found?
How do you calculate the RMS value?
VRMS = VPEAK / Square root 2
What is the equation to find out V peak
Vpeak = √2 Vrms
Also, since V = IR where R is a constant, this extends to current too. What is the I peak involving Current
Ipeak = √2 Irms
The r.m.s. value of an a.c. supply is equal to what?
a d.c. supply value which gives the same power output.
What is the voltage of a mains supply in UK?
The voltage of 230 volts
Definition of charge?
Current is defined as the flow of electric charge per second.
The equation to find out the charge?
I= Q/t
Current (Amperes) = Charge(Coulombs)/ Time(Seconds)
That means 1 coulomb is equal to 6.25x1018 electrons.
True or False?
True
What is the definition of voltage (potential difference)?
‘Potential Difference’ as the number of joules of work energy needed to drive each coulomb of charge from one point in the circuit to another.
1 volt is equal to
1 joule for every coulomb of charge.
This gives us the relationship:
V = Ew/Q
or Ew = QV
Ohm’s Law
If you increase the voltage (potential difference) across a component in a circuit with resistance R, the current through it will do what?
What does the gradient of the graph equal?
What equation do you get out of it? (v=Something)
increase in direct proportion
Resistance
V=IR
OHM’s Law
If the resistance is not constant V and I are no longer what?
What does the graph look like?
directly proportional the line of best fit will not longer be straight
What does power mean?
Energy transformed per second.
What are the 4 power equations?
P = E/t
P = IV
P = I^2 R
P = V2/R
Current Series equation
IS = I1 = I2 = I3
Current Parallel equation?
Ip = I1 + I2 + I3
Voltage series equation
VS = V1 + V2 + V3
Voltage parallel equation?
VS = V1 = V2 = V3
Resistance series equation?
Rs=R1+R2+R3