DC Circuit Flashcards
(20 cards)
What is Electromotive Force (EMF)?
The amount of energy given to each coulomb of charge to go around the circuit once.
What is Potential Difference (p.d.)?
Work done per unit charge; energy transformed from electrical to other forms per unit charge.
What is the difference between EMF and p.d.?
EMF is energy supplied to the circuit per unit charge; p.d. is energy used per unit charge.
What is Internal Resistance?
Resistance inside the power source that reduces the p.d. when current flows.
What equation defines voltage across a resistor?
V = IR
What equation defines voltage lost due to internal resistance?
V = E − Ir
What is the total EMF equation in a circuit with internal resistance?
E = IR + Ir
Rearranged EMF equation factoring total resistance:
E = I(R + r)
What is Kirchhoff’s First Law?
Sum of currents into a junction = sum of currents out; conservation of charge.
What is Kirchhoff’s Second Law?
Sum of EMFs = Sum of potential differences in a closed loop; conservation of energy.
Effective resistance in series?
R = R1 + R2 + … + Rn
Effective resistance in parallel?
1/R = 1/R1 + 1/R2 + … + 1/Rn
What is a potential divider?
A circuit that splits voltage into smaller parts using resistors.
How does a thermistor behave in a potential divider?
Resistance decreases as temperature increases.
How does an LDR behave in a potential divider?
Resistance decreases as light intensity increases.
What is a potentiometer?
A continuously variable potential divider used to compare potential differences.
How is p.d. related to length in a potentiometer wire?
Potential difference is proportional to the length from the reference point.
Use of potentiometer to compare EMFs?
Move the slider until the galvanometer reads zero; use length ratio to compare EMFs.
Formula to compare EMFs using potentiometer:
E1/E2 = L1/L2
If E1 = 10 V, XY = 1 m, XT = 0.4 m, what is E2?
E2 = (0.4/1.0) × 10 = 4 V
