Chapter 5 - Circuit Rules Flashcards
Describe the distribution of potential difference across components in parallel.
The pd across components in parallel is the same.
What is the total resistance of a circuit containing two 500ohm resistors in parallel?
Using the 1/R rule, total resistance = 250ohms.
How do you calculate the rate of heat transfer for an electrical device?
Rate of heat transfer is the same as power. P = I x V or I^2R or V^2/R
What is internal resistance?
Loss of potential difference (lost volts) per unit current in the source when current passes through it.
No current, no lost volts.
Define potential difference across a power source.
Electrical energy per unit charge delivered by the source when it is in a circuit.
Define emf, electromotive force.
The electrical energy per unit charge produced by the source.
What happens to the lost volts across a power source with internal resistance when the external resistor connected to the circuit increases in resistance?
The lost volts decreases as the external resistor increases in resistance the current in the circuit (and through the power source) decreases. This causes Ir to decrease and so less lost volts.
Describe how the potential difference is distributed to components in a series circuit.
The total pd across all components is equal to the sum of the pd across each component.
The potential difference across and current through a power source is measured as the resistance of a variable resistor connected to the power source is changed. How is the emf and internal resistance of the power source determined from these values?
A pd current graph is plotted and a best fit line added. The y-intercept is the emf of the power source and the gradient corresponds to the internal resistance of the power source.
Two cells are connected in series with values 5V and 8V. The 5V cell is arranged in reverse polarity to the 8V cell. What is the net emf of the cells?
3V in the direction of the 8V cell.
Describe the make up of a potential divider circuit.
Two or more resistors in series connected to a source of fixed potential difference.
A fixed resistor and thermistor are connected in series. The thermistor is slowly warmed. Across which resistor should the voltmeter be placed in order to get a larger pd with increasing temperature?
The voltmeter should be placed across the fixed resistor.
Describe why the potential difference across a thermistor in a potential divider circuit decreases as the temperature of the thermistor increases.
As the thermistor gets warmer its resistance decreases.
This increases the current in the circuit.
A larger current through the fixed resistor means a greater pd across it, meaning a lower proportion of pd available to the thermistor.
State and explain why it is an advantage for a rechargeable battery to have a low internal resistance.
It will have a faster charge time due to a larger current flow through it.
What is meant by an ohmic conductor?
A component with a constant resistance.
