 # 2 Electricity – Part C “Energy and Voltage”

### Aims…

2.7 explain why a series or parallel circuit is more appropriate for particular applications, including domestic lighting

2.8 understand how the current in a series circuit depends on the applied voltage and the number and nature of other components

2.9 describe how current varies with voltage in wires, resistors, metal filament lamps and diodes, and how this can be investigated experimentally

2.10 describe the qualitative effect of changing resistance on the current in a circuit

2.11 describe the qualitative variation of resistance of light-dependent resistors (LDRs) with illumination and of thermistors with temperature

2.12 know that lamps and LEDs can be used to indicate the presence of a current in a circuit.

2.13 know and use the relationship between voltage, current and resistance:

voltage = current × resistance    V = I × R

2.14 know that current is the rate of flow of charge

2.15 know and use the relationship between charge, current and time:

charge = current × time        Q = I × t

2.16 know that electric current in solid metallic conductors is a flow of negatively charged electrons

2.17 understand why current is conserved at a junction in a circuit

2.18 know that the voltage across two components connected in parallel is the same

2.19 calculate the currents, voltages and resistances of two resistive components connected in a series circuit

2.20 understand that: voltage is the energy transferred per unit charge passed the volt is a joule per coulomb

2.21 know and use the relationship between energy transferred, charge and voltage:

Energy transferred = charge x voltage. E = Q x V.

Resources….

## Daniell cell - Volt Defined

The Daniell cell is a type of electrochemical cell invented in 1836 by John Frederic Daniell, a British chemist and meteorologist, and consisted of a copper pot filled with a ...copper sulfate solution, in which was immersed an unglazed earthenware container filled with sulfuric acid and a zinc electrode. He was searching for a way to eliminate the hydrogen bubble problem found in the voltaic pile, and his solution was to use a second electrolyte to consume the hydrogen produced by the first. Zinc sulfate may be substituted for the sulfuric acid. The Daniell cell was a great improvement over the existing technology used in the early days of battery development. A later variant of the Daniell cell called the gravity cell or crowfoot cell was invented in the 1860s by a Frenchman named Callaud and became a popular choice for electrical telegraphy.
The Daniell cell is also the historical basis for the contemporary definition of the volt, which is the unit of electromotive force in the International System of Units. The definitions of electrical units that were proposed at the 1881 International Conference of Electricians were designed so that the electromotive force of the Daniell cell would be about 1.0 volts. With contemporary definitions, the standard potential of the Daniell cell at 25 °C is actually 1.10 V