Physics - Voltage and Potential Difference
OCR A-Level Physics 2022
Potential energy and definitions
How does a stretched elastic band have the potential to do work?
When it is released it will move.
What is potential difference?
The energy transferred per unit charge from electrical energy to another form of energy.
When used to measure a component, what does potential difference measure?
The difference in energy in the charge carriers before and after going through the component.
EMF
What is EMF?
The energy transferred per unit charge into electrical energy from another store of energy.
Instead of measuring force, what does EMF measure?
Energy given to charge carriers.
Units and distinguishing p.d. from EMF
What is the difference between potential difference and EMF?
- Potential difference measures the energy transferred by charge carries.
- EMF measures the energy transferred to charge carries.
Some energy is transferred from a chemical reaction inside a battery to the charge carriers in a circuit. Is this potential difference or EMF?
EMF.
Some electrical energy is transferred from a charge carrier to kinetic energy inside a motor in a circuit. Is this potential difference or EMF?
Potential difference.
Kirchhoff’s Second Law
What is Kirchhoff’s Second Law?
The sum of voltages across components that supply electrical energy must equal the sum of voltages across all other components in the same loop.
How could you summarise Kirchhoff’s 2nd Law using $\sum$?
Symbol formulae
What is thermionic emission?
The emission of electrons when something is heated up.
Electronvolts and electron speed
What is an electronvolt?
The energy transferred on an electron when it accelerates through a potential difference of $1V$.
What is the formula for work done ($W$) in terms of a potential difference $V$ and a charge $Q$?
How can you work out the speed of an electron?
Equate it’s energy to $\frac{1}{2}mv^2$.
What is the potential difference of the unlabelled component?