4.2 Energy, power and resistance Flashcards
What is the definition of electromotive force?
The energy gained per unit charge by passing through the supply, when a form of energy is transferred to electrical energy carried by the charges.
What is the definition of potential difference?
The energy transferred per unit charge by the charges passing through the component.
What are e.m.f and p.d both measured in?
Volts (v) or joules per coulomb (JC^-1).
Where is e.m.f measured?
At a supply.
Where is p.d measured?
Across a component.
What is the equation for e.m.f?
e.m.f = energy transferred / charge
What is the equation for p.d?
p.d = work done / charge
What are e.m.f and p.d measured by?
A voltmeter connected in parallel with a supply or component.
What happens when an electron is accelerated by a voltage?
The electron gains energy equal to eV, this energy is also equal to the kinetic energy of an electron, Ek = 1/2mv^2.
What is the resistance of an ammeter assumed to be?
Very small so that it doesn’t affect the circuit.
What is the resistance of a voltmeter assumed to be?
Very high so that it doesn’t affect the circuit.
What is Kirchhoff’s second law?
Around any series circuit, the sum of the e.m.fs is equal to the sum of the p.ds.
How do current and voltage behave in a series circuit?
Current is the same at any point, voltage splits up over each component.
How do current and voltage behave in a parallel circuit?
Current splits up down each branch, voltage is the same across each branch.
What is the equation for resistance?
Resistance = voltage / current
