Topic 3.2-Complete Electrical Circuits Flashcards
How does current flow in series and parallel?
Series= constant
Parallel= Itotal= I1 + I2 +…
How is voltage distributed in series and parallel?
Series= Vtotal= V1 + V2 + …
Parallel= Constant for each branch
How is resistance distributed in series and parallel?
Series= Rtotal= R1 + R2 +…
Parallel= 1/Rtotal= 1/R1 + 1/R2 +…
Derive resistance in series:
Vtotal= V1 + V2
Vtotal= I x Rtotal
V1= IR1 and V2=IR2
so… IRtotal= IR1 + IR2
Cancel current: Rtotal= R1 + R2
Derive resistance in parallel:
Itotal= I1 + I2
Itotal= V/Rtotal
I1= V/R1 and I2= V/R2
so… V/Rtotal= V/R1 + V/R2
Cancel voltage: 1/Rtotal= 1/R1 + 1/R2
Give the equation for total resistance in parallel:
Rtotal= (R1 x R2)/ (R1 + R2)
What is Kirchoff’s first law?
The sum of the currents leaving a point is the same as the sum of the currents entering that point.
What is Kircoff’s second law?
Around any closed loop, the sum of the EMFs is equal to the sum of the PDs.
What is the potential divider equation?
Vout= Vin x R2/ (R1 +R2)
What is a potential divider?
A sries circuit that produces an output voltage that is a fraction of its input voltage.
What are the uses of potential dividers?
Anything that requires a variable voltage or a voltage that differs from the input. For example, light activated switches.
What is a potentiometer?
A variable voltage supply which uses a movable contact ‘wiper’ to move along a fixed length of resistance wire and alter the lengths of each segment, providing a variable voltage.
Define terminal p.d:
The voltage across the terminals of a battery.
Define internal resistance:
The resistance of an EMF source. They can be thought of as the flow of current inside the power supply.
What is the equation for internal resistance?
Vinternal= Ir
What are lost volts?
The internal p.d of a power source, found using the equation:
Vterminal= Vload = EMF -Ir
What is the equation for EMF, considering energy conservation?
EMF= Vload + Vinternal
What is a short circuit?
A circuit where the only significant resistance is the internal resistance.
What is the equation for short circuit current?
Current= EMF/ Internal resistance
Why might a power supply have a high large internal resistance?
To avoid supplying too much current, especially in a high voltage supply.
What are the 5 equations for power in circuits?
Power= energy/ time
Power= work done/ time
Power= current x voltage
Power= current2 x resistance
Power= voltage2 / resistance
What is the equation for efficiency (power or energy)?
Eff. = useful energy (or power) out / total energy (or power) in
