Conservaion Of Charge & Energy In A Circuit + Potential Dividers Flashcards
Is it correct that charge is conserved?
Yes
The amount of charge flowing into a junction is [……….] to the charge flowing out of that junction.
Equal
Define Current?
Rate of flow of charge
Because Current is Rate of Flow of charge and charge is the same when entering and exiting a junction what equation can we derive?
I1 = I2 + I3
What is Kirchhoffs 1st Law?
The total current entering a junction = the total current leaving it
Energy is [……..]
Conserved
What two variables must be equal in a closed loop for energy to be conserved ?
E.M.F and Potential Difference
What is Kirchhoffs 2nd Law?
The total E.M.F around a series circuit = the sum of the PD’s across each component
What is the Resistance equation for a Series Circuit?
R (total) = R1 + R2 + R3
Derive the equation R (total) = R1 + R2 + R3
1 - Current is the same at all points because there are no junctions in a series circuit
2 - E.M.F split between components (Kirchhoffs 2nd Law) e = V1 + V2 + V3
3 - V = IR so if I is constant
IR (total) = IR 1 + IR2 + IR3
4 - Cancel Out I gives R (total) = R1 + R2 + R3
What is the equation for resistors in parallel?
1 / R (total) = 1 / R1 + 1 / R2 + 1 / R3
How do you derive the equation for resistors in parallel? 1 / R (total) = 1 / R1 + 1 / R2 + 1 / R3
1 - Current is split at each junction so : I = I1 + I2 + I3
2 - PD is constant in a parallel circuit so the PD is the same
3 - V / R (total) = V / R1 + V / R2 + V / R3
4 V is constant so cancelling V Gives
1 / R (total) = 1 / R1 + 1 / R2 + 1 / R3
What do you use a Potential Divider for?
To get a fraction of a source voltage
What would the potential divider read if you had a 2 Ω resistor and a 3 Ω resistor?
- You would get 2/5 of the PD’s across the 2 Ω Resistor
- and 3/5 across the 3 Ω resistor
What is the Potential Divider Equation?
V (out) = ( R2 ) / ( R1 + R2 )
You can use a variable resistor to vary….
Vary the voltage
If you increase R1 in a series circuit does the V (our) get bigger or smaller?
Smaller
What does LDR stand for?
Light dependant resistor
Does an LDR have a high or low resistance in the dark?
High resistance in the dark
Does an LDR have a high or low resistance in the light?
Low resistance
An NTC thermistor has a high resistance at […..] temperatures
Low
An NTC thermistor has a low resistance at [……] temperatures
Low
What is a Potentiometer?
Is a potential divider with a variable resistor replacing R1 and R2
How does a Potentiometer work?
Move a slider or turn a knob to adjust the relative sizes of R1 and R2 that way you can vary V out from 0V up to the source voltage
Where are potentiometers used?
For volume control on a speaker
