# Physics - Voltage and Potential Difference

> Source: https://ollybritton.com/notes/a-level/physics/topics/potential-difference/ · Updated: 2021-01-18 · Tags: physics, electricity, year-1, school

### 2021-01-18
##### What does "potential energy" mean??
The potential to do work.

##### 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 transfered 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.

##### What does EMF stand for??
Electromotive force.

##### What is EMF??
The energy transfered per unit charge into electrical energy from another store of energy.

##### Instead of measuring force, what does EMF measure??
Energy given to charge carriers.

##### What are the units for potential difference??
Volts, $V$

##### What are the units for EMF??
Volts, $V$

##### 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.

##### What does a voltage of $100V$ mean??
100J are tranfered per couloumb of charge.

##### What is $1V$ in terms of $J$ and $C$??
$$
1V = 1JC^{-1}
$$

##### Some energy is transfered 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 transfered from a charge carrier to kinetic energy inside a motor in a circuit. Is this potential difference or EMF??
Potential difference.

##### What is Kirchoff'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 Kirchoff's 2nd Law using $\sum$??
$$
\sum \text{p.d.} = \sum \text{e.m.f.}
$$

##### What is the symbol formula for EMF??
$$
E = \frac{W}{Q}
$$

##### What is the symbol formula for potential difference??
$$
V = \frac{W}{Q}
$$

##### What is themionic emission??
The emmision of electrons when something is heated up.

##### 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 $Q$??
$$
W = VQ
$$

##### Since $W = VQ$, what is one electronvolt in Joules??
$$
1.6\times10^{-19}J
$$

##### What does an electronvolt measure??
Energy.

##### How can you work out the speed of an electron??
Equate it's energy to $\frac{1}{2}mv^2$.

##### What is the formula for the energy transfered to a single electron travelling from a cathode to an anode over a potential difference of $V$??
$$
eV
$$

##### If an electron has energy $eV$, what could you set it equal to work out the electron's velocity??
$$
eV = \frac{1}{2}mv^2
$$

### 2021-01-20
##### ![PHOTO PD UNLABELLED 7V](pd-unlabelled-7v.png) What is the potential difference of the unlabelled component??
$$
7V
$$

##### ![PHOTO PD UNLABELLED 20V](pd-unlabelled-20v.png) What is the potential difference of the unlabelled component??
$$
20V
$$

---
Olly Britton — https://ollybritton.com. Machine-readable index: https://ollybritton.com/llms.txt