(ii) [tex]V=I R[/tex]
[tex]\Rightarrow \quad R=\frac{V}{I}=\frac{1.5}{0.5}=3 \Omega[/tex]
Question 34 (WASSCE Nov 2017 Ou 5d)
State two ways in which parallel wiring system in households is important.
ii) The power rating of an electric stove is 2 kW. Calculate the amount of energy it uses in 1 hour.
Answer (2)
Identify the given values: Power P = 2 kW and time t = 1 hour .
Use the formula E = P × t to find the energy.
Calculate the energy in kilowatt-hours: E = 2 kW × 1 hour = 2 kWh .
The electric stove uses 2 kWh of energy in 1 hour.
Explanation
Understanding the Problem Let's break down this problem step by step so you can fully understand how to calculate the energy used by an electric stove.
Identifying Given and Required Information First, we need to identify what information we have and what we need to find:
Given:
Power rating of the electric stove, P = 2 kW = 2000 W (since 1 kW is 1000 W).
Time the stove is used, t = 1 hour .
Find:
The amount of energy, E , used by the electric stove in that 1 hour.
Stating the Formula The formula that relates power, energy, and time is:
E = P × t
Where:
E is the energy used (typically in Joules or kilowatt-hours).
P is the power (in Watts or kilowatts).
t is the time (in seconds or hours).
Calculating the Energy Now, let's plug in the values we have into the formula. We'll calculate the energy in two different units to give you a better understanding.
1. Calculating Energy in Joules:
Since the power is given in Watts (W) and we want the energy in Joules (J), we need to convert the time to seconds:
t = 1 hour = 1 × 60 minutes = 60 minutes = 60 × 60 seconds = 3600 seconds
Now we can calculate the energy:
E = 2000 W × 3600 s = 7 , 200 , 000 J
So, the electric stove uses 7,200,000 Joules of energy in 1 hour.
2. Calculating Energy in Kilowatt-hours:
Since the power is given in kilowatts (kW) and we want the energy in kilowatt-hours (kWh), we can directly use the time in hours:
E = 2 kW × 1 hour = 2 kWh
So, the electric stove uses 2 kilowatt-hours of energy in 1 hour.
Final Answer The amount of energy the electric stove uses in 1 hour is 7,200,000 Joules, which is also equal to 2 kilowatt-hours.
Examples
Imagine you're planning a camping trip and need to power a small electric heater rated at 500W for 4 hours each night. By calculating the energy consumption, you can determine the size of the portable generator or battery pack you'll need. Knowing that E = P × t , you find E = 0.5 kW × 4 hours = 2 kWh per night. Over a 3-night trip, you'd need 6 kWh of energy, helping you choose the right equipment and avoid running out of power.
In households, parallel wiring systems are important because they allow devices to operate independently and ensure consistent voltage across appliances. The electric stove with a power rating of 2 kW uses 2 kWh of energy when operated for 1 hour. This calculation helps in understanding energy consumption for household budgeting and efficiency.
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