Electromotive Force (e.m.f) Quiz & Flashcards

What is the definition of electromotive force (e.m.f)?

How is electromotive force (e.m.f) represented?

Why does a cell become warm after a period of time?

How is e.m.f measured using a voltmeter?

What happens to the voltage over time in a power supply due to internal resistance?

How can a cell be conceptually viewed in terms of e.m.f and internal resistance?

What does the terminal potential difference represent in a cell?

What would happen to the terminal p.d if a cell had no internal resistance?

What is the definition of 'lost volts' in a cell due to internal resistance?

Which equation represents 'lost volts' in a cell according to Ohm's law?

Why is the terminal p.d always lower than the e.m.f in a cell?

What does 'lost volts' represent in a cell circuit?

Electromotive Force (e.m.f)

Defined as the energy per unit charge supplied by a cell or battery in an electrical circuit.
Represented by the symbol E and measured in volts (V).

Cell Heating

A cell generates heat after prolonged use due to internal resistance, leading to energy dissipation.

Measuring e.m.f

To measure e.m.f, a voltmeter is connected across the terminals of a cell without drawing current, ensuring an accurate reading of potential difference.

Voltage and Internal Resistance

Over time, the voltage in a power supply decreases due to internal resistance causing a voltage drop as current flows.

Conceptual View of a Cell

A cell can be viewed as having an electromotive force (e.m.f) and an internal resistance, which together influence the performance of the cell in a circuit.

Terminal Potential Difference (p.d)

Terminal p.d represents the voltage available at the cell terminals when current flows, reflecting the effective energy supplied to the external circuit.

Impact of No Internal Resistance

If a cell had no internal resistance, the terminal potential difference would equal the e.m.f, resulting in maximum efficiency in voltage delivery.

Lost Volts

'Lost volts' refers to the voltage drop that occurs within the cell due to internal resistance when current flows.

Equation for Lost Volts

According to Ohm's law, lost volts is calculated as ( I \times r ), where I is the current and r is the internal resistance.

Terminal p.d vs. e.m.f

The terminal potential difference is always lower than the e.m.f because of energy lost to internal resistance when current is drawn.

Significance of Lost Volts

'Lost volts' represent the energy wasted in overcoming internal resistance, indicating inefficiencies within the circuit.

Test your knowledge on electromotive force (e.m.f) in the context of AS & A Level Physics. Understand the concept of e.m.f as the amount of chemical energy converted to electrical energy per coulomb of charge passing through a power supply, typically represented by the symbol ε (epsilon) and measured in volts.