What does e.m.f. stand for in electrical circuits?
Electromotive Force, which is the total potential difference available from the cell.
What is internal resistance in a cell?
The resistance within the cell that causes a potential drop.
What are ‘lost volts’?
The potential difference across the internal resistance of the cell that is not available for external use.
What is terminal potential difference (t.p.d.)?
The potential difference available at the terminals of the cell.
What is the relationship between e.m.f., lost volts, and t.p.d.?
E.m.f. = Lost Volts + Terminal Potential Difference.
What is an ‘ideal cell’?
A cell that has zero internal resistance and therefore no lost volts.
How is the e.m.f. of a cell measured?
By placing a voltmeter across the cell when no current is flowing.
What happens to t.p.d. as external resistance decreases?
The t.p.d. decreases while lost volts increase as current increases.
What is the formula relating e.m.f., internal resistance, and external resistance?
E = I(R + r), where E is e.m.f., I is current, R is external resistance, and r is internal resistance.
How can the internal resistance of a cell be calculated from a graph of t.p.d. against current?
The gradient of the graph gives the internal resistance; r = -gradient.
What occurs when a cell is short-circuited?
The only resistance in the circuit is the internal resistance, which can cause the cell to overheat.
What is the effect of increasing current on lost volts?
Increasing current results in higher lost volts due to increased flow through the internal resistance.
What is the formula for calculating lost volts?
Lost Volts = I * r, where I is current and r is internal resistance.
What happens to the voltage across the cell when the switch is open?
The voltage reading will equal the e.m.f. of the cell.
How do you find the current in a short-circuited cell?
Use the formula I = V / r, where V is the e.m.f. and r is the internal resistance.
What is the significance of the intercept on the vertical axis of a t.p.d. vs. current graph?
It represents the e.m.f. of the cell.
What does a higher internal resistance imply about a cell’s performance?
It indicates more energy is lost as heat, reducing the efficiency of the cell.
How does the behavior of internal resistance affect circuit analysis?
Internal and external resistances are treated as series resistors, affecting total voltage and current.
What is the impact of increasing the internal resistance on the overall circuit?
It decreases the terminal potential difference available for external components.
What is the relationship between e.m.f. and the voltage across the cell when no current is drawn?
The voltage across the cell equals the e.m.f. when no current flows.
What happens to the t.p.d. when the external resistance is decreased?
The t.p.d. decreases as the current increases, leading to more lost volts.
What is the formula for calculating the total resistance in a circuit with both internal and external resistances?
Total Resistance = R + r, where R is external resistance and r is internal resistance.
What is the effect of short-circuiting a cell on its internal resistance?
It causes the internal resistance to be the only resistance in the circuit, leading to high current and potential overheating.
