**I/GCSE Physics**** Question Analysis Topic: Chapter 2: Electricity - Mains Electricity Part 3**

For I/GCSE Physics, you should know:

Let's dive into the last part of IGCSE Physics Chapter 2 sub-topic of Mains Electricity, focusing on the relationship between power, current, and voltage, as well as the differences between alternating current (AC) and direct current (DC).

__The Relationship between Power, Current, and Voltage__:

In the context of electricity, the relationship between power (P), current (I), and voltage (V) is described by the formula: **P = I × V**. This equation is known as the power equation and is a fundamental principle in electrical circuits.

Power (P) is the **rate** at which electrical energy is transferred or consumed. It is measured in watts (W). Current (I) is the **flow** of electric charge, measured in amperes (A). Voltage (V) is the **potential difference** across a component, measured in volts (V).

The power equation, P = I × V, can be used to calculate the power in an electrical circuit, given the values of current and voltage. Alternatively, it can be used to determine the current or voltage if the other two quantities are known.

__Applying the Power Equation to Fuse Selection__:

Fuses are essential safety devices used in electrical circuits to **protect against overcurrent**. They are designed to **break the circuit when the current exceeds a certain limit**, preventing damage to the circuit and potential fire hazards.

To select an appropriate fuse for a particular circuit, you can use the power equation to determine the required fuse rating. The steps are as follows:

- Determine the power consumption of the electrical appliance or device.
- Measure or calculate the voltage (V) of the mains electricity supply.
- Use the power equation, P = I × V, to calculate the current (I) flowing through the circuit.
- Select a fuse with a rating
**slightly higher**than the calculated current value to ensure proper protection.

This approach ensures that the fuse is rated correctly for the specific circuit and can effectively interrupt the flow of current in the event of an overload or short circuit.

__Alternating Current (AC) vs. Direct Current (DC)__:**Mains** electricity supplied to our homes and buildings is typically in the form of **alternating** current (AC), whereas the electricity supplied by a cell or **battery** is **direct** current (DC).

__Alternating Current (AC)__:

- In AC, the flow of electric charge (current)
**periodically reverses direction**. - The
**voltage**in AC also**varies sinusoidally**over time, with the positive and negative polarities alternating. - AC is the
**standard form of electricity distribution**and is used for most household and industrial applications.

__Direct Current (DC)__:

- In DC, the flow of electric charge (current) is
**unidirectional**, flowing in a single direction. - The voltage in DC remains
**constant**, with a fixed positive and negative polarity. - DC is commonly used in
**portable electronic devices**, such as smartphones, laptops, and flashlights, powered by batteries or solar cells.

The key difference between AC and DC is the way the electrical charge flows.** AC allows for more efficient transmission of power over long distances, while DC is better suited for certain applications, such as powering electronics and charging batteries**.

Work hard for your I/GCSE Physics examination!

End of analysis. Great!