Physics - Recall for Chapter 10: Electrical Circuits
OCR A-Level Physics 2022
Recall Questions
Kirchhoff’s laws and series/parallel rules
State Kirchhoff’s second law and appreciate that this is a consequence of conservation of energy?
Sum of the EMF is equal to the sum of the voltages.
What can we say about the current through a component in series?
Same for each component.
What can we say about the p.d. across parallel branches in a circuit?
It is the same for each branch.
How do you find the total EMF from cells connected in series with the same polarity?
Their EMFs are added.
Combining resistors
How do you calculate the total resistance of resistors in series?
Sum of the individual resistance.
How does the total resistance change when a resistor is added in series?
It always increases.
How does the total resistance change when a resistor is added in parallel?
It always decreases.
What is the effect of connecting two identical resistors in parallel?
Resistance is halved.
What is the effect of connecting two identical resistors in series?
Resistance is doubled.
Internal resistance and EMF
What is internal resistance?
The opposition to current created by the charge carriers having to flow through the source of EMF.
What are the lost volts for a power supply?
The p.d. dropped across the internal resistance.
What is the relationship between EMF, terminal p.d. and lost volts?
EMF = terminal p.d. + lost volts
How do you find the internal resistance from a graph of terminal p.d. against current?
Negative of the gradient.
Potential dividers
What is a potential divider?
Two or more resistance in series with a fixed source of EMF.
What determines the ratio of the p.d. across the resistors in a potential divider?
It is equal to the ratio of their resistances.