Reading Time: 2 minutes
Electric Circuits: Understanding Current, Voltage, and Resistance in A-Level Science
What Are Electric Circuits?
Electric circuits are pathways that allow the flow of electric current, driven by a voltage source.
Key Concepts in Electric Circuits
Electric Current (I)
The flow of electric charge through a conductor:
![\[ I = \frac{Q}{t} \]](https://skinattuition.co.uk/core/ql-cache/quicklatex.com-028143c96245eab7e18597965435280a_l3.png "Rendered by QuickLaTeX.com")
Where:
: Current (A)
: Charge (C)
: Time (s)
: Current (A)
: Charge (C)
: Time (s)Voltage (V)
Voltage is the potential difference across a component, driving the flow of charge.
Resistance (R)
Resistance opposes the flow of current:
![\[ R = \frac{V}{I} \]](https://skinattuition.co.uk/core/ql-cache/quicklatex.com-cc7bd10c66942bb81523fe94285354c9_l3.png "Rendered by QuickLaTeX.com")
Ohm’s Law
Ohm’s Law relates voltage, current, and resistance:
![\[ V = IR \]](https://skinattuition.co.uk/core/ql-cache/quicklatex.com-a85f81cda843a8fb5d4a3d02ca73a0a0_l3.png "Rendered by QuickLaTeX.com")
Series and Parallel Circuits
Series Circuits
- The current is the same through all components
- Total resistance:
Parallel Circuits
- Voltage is the same across all components
- Total resistance:
Example Problem
A circuit has a 
battery connected to two resistors (
, 
) in series. Find the total resistance and current.
- Total Resistance:
![\[ R_{\text{total}} = R_1 + R_2 = 4 + 6 = 10 \, \Omega \]](data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHdpZHRoPSIyNDkiIGhlaWdodD0iMTUiIHZpZXdCb3g9IjAgMCAyNDkgMTUiPjxyZWN0IHdpZHRoPSIxMDAlIiBoZWlnaHQ9IjEwMCUiIHN0eWxlPSJmaWxsOiNjZmQ0ZGI7ZmlsbC1vcGFjaXR5OiAwLjE7Ii8+PC9zdmc+ "Rendered by QuickLaTeX.com")
- Current:
![\[ I = \frac{V}{R_{\text{total}}} = \frac{12}{10} = 1.2 \, \text{A} \]](data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHdpZHRoPSIxODciIGhlaWdodD0iMzkiIHZpZXdCb3g9IjAgMCAxODcgMzkiPjxyZWN0IHdpZHRoPSIxMDAlIiBoZWlnaHQ9IjEwMCUiIHN0eWxlPSJmaWxsOiNjZmQ0ZGI7ZmlsbC1vcGFjaXR5OiAwLjE7Ii8+PC9zdmc+ "Rendered by QuickLaTeX.com")
![\[ R_{\text{total}} = R_1 + R_2 = 4 + 6 = 10 \, \Omega \]](https://skinattuition.co.uk/core/ql-cache/quicklatex.com-c63f3888368c465ec30c14c72bf12234_l3.png "Rendered by QuickLaTeX.com")
![\[ I = \frac{V}{R_{\text{total}}} = \frac{12}{10} = 1.2 \, \text{A} \]](https://skinattuition.co.uk/core/ql-cache/quicklatex.com-fb4703d2a81118f7e98d49f048514f70_l3.png "Rendered by QuickLaTeX.com")
Applications of Electric Circuits
Electronics
- Powering devices like smartphones and computers
Medical Equipment
- Used in ECG machines to monitor heart activity
Renewable Energy
- Managing power distribution in solar energy systems
Common Mistakes in Circuit Calculations
- Mixing up series and parallel formulas for resistance
- Forgetting units (
, V, A) - Misinterpreting current directions in complex circuits
, V, A)Practice Questions
- A
battery powers a 
resistor. Calculate the current. - Explain the differences between series and parallel circuits.
- Describe one application of Ohm’s Law in electronics.
battery powers a 
resistor. Calculate the current.