Electrical circuits

Question 1

What is a series circuit?

Answer 1

A series circuit contains just one loop, around which an electric current can flow. Current is the same at all points. The potential difference is shared between components and total resistance = sum of individual resistances.

Question 2

What is a parallel circuit?

Answer 2

A parallel circuit contains more than one loop, and the current will split up between branches or recombine at the junctions. Potential difference is the same across each branch, and adding more branches reduces total resistance.

Question 3

How is current measured in series and parallel circuits?

Answer 3

Ammeter:
Series - same current everywhere. To measure it, you put the ammeter in series with the component.
Parallel - current splits between branches. To measure current in a branch, you put the ammeter in series in that branch.

Question 4

How is potential difference measured in series and parallel circuits?

Answer 4

Voltmeter:
Series - voltage is shared between components. To measure the voltage across a component, you put the voltmeter in parallel with that component.
Parallel - voltage across each branch is the same as the supply. A voltmeter is still connected in parallel with the component or branch.

Question 5

What examples are there of energy transfers in electrical devices?

Answer 5

Filament lamp: electrical to heat + light
Motor: electrical to kinetic
Heater: electrical to thermal

Question 6

How do you determine the relationship between potential difference, current and resistance for a resistor and a filament lamp when arranged in series and parallel?

Answer 6

Circuit set-up-
1) Ammeter in series.
2) Voltmeter in parallel.
3) Variable resistor.
4) Component under test (resistor or filament lamp).
5) Power supply - start on low voltage for safety.

Method:
1) Build the circuit with the component you’re testing.
2) Adjust the variable resistor to change the voltage gradually.
3) For each setting record current and potential difference.
4) Take at least 6-8 readings across a range of voltages.
5) Reverse the power supply connections to obtain negative results.
6) Plot a graph of current against potential difference.

Question 7

What are the expected results and graph shapes for the relationship between potential difference, current and resistance for a filament lamp and a resistor?

Answer 7

Resistor - straight line through the origin. This is because current is directly proportional to voltage; resistance stays constant. This is because the temperature does not change significantly.

Filament lamp - curved; gets shallower at higher voltages. This is because as current increases, the filemant heats up. Hotter filament = higher resistance, so current increases less for each extra volt.

Question 8

For investigation of relationship between current, potential difference and resistance using a filament lamp and a resistor, why will series and parallel circuits both lead to the same shape of graph for both components?

Answer 8

Current will flow through the components in either arrangement, with the shape of the graph being determined by the structure of the component and whether it obeys Ohm’s law or not, not on how it is arranged in a circuit, since heat will still be dissipated in each circuit.