Calculating electrical energy and costs in Grade 9 Physics is pretty easy once you learn the basics! Let’s break it down into simple parts.

Basic Concepts

1. Voltage (V): This is the difference in power in an electrical circuit. It's measured in volts (V).

2. Current (I): This is how much electric charge is flowing. It is measured in amperes (A).

3. Resistance (R): This shows how much a material slows down the flow of electricity. It's measured in ohms (Ω).

Formula for Electrical Power

To find the power (P) in an electrical circuit, we can use this formula:

$$P = V \times I$$

Here, power is measured in watts (W). If you know the voltage and current, you can quickly find the power being used.

Calculating Energy Consumption

To figure out how much energy an electrical device uses, we use this formula:

$$E = P \times t$$

Where:

• $E$ is energy, which can be measured in joules (J) or kilowatt-hours (kWh).
• $t$ is time, which is measured in hours (h).

Remember, 1 kilowatt-hour equals 3.6 million joules!

Cost Calculation

To calculate how much using electrical energy will cost, you need to know how much your electric company charges, usually in cents per kWh. Once you know how much energy your device uses, you can find the cost with this formula:

$$\text{Cost} = E \times \text{Rate}$$

Example

Let’s say you have a 60 W light bulb and you use it for 5 hours. First, we will find the energy:

1. Power = 60 W (which is the same as 0.06 kW)
2. Time = 5 h
3. Energy = $0.06 \, kW \times 5 \, h = 0.3 \, kWh$

If your rate is $0.12 per kWh, then:

$$\text{Cost} = 0.3 \, kWh \times 0.12 = 0.036$$

That’s a simple overview of calculating electrical energy and costs! Knowing this can help you understand your electricity bills better.