Introduction
- It is a fundamental concept in physics, and we learn the concept of energy because it helps us understand and explain how the physical world works.
- Energy is transferred whenever things happen and the transferred of energy by a force is called work done.
- When energy is transferred by doing work, it causes things to happen — like moving an object, heating something etc.
Real-life Examples:
What is Energy?
- Energy is the ability to do work or cause change.
- It exists in various forms like- kinetic, potential, thermal, etc.
- It is measured in joules (J).
Real-life examples of energy in different forms:
1. Electrical Energy
- A fan runs using electricity and electric current powers the motor to rotate the blades.
2. Thermal Energy
- Boiling water on a stove and heat energy from the flame increases the temperature of water.
3. Kinetic Energy
- A moving car or a running person and objects in motion have kinetic energy.
How Power is related to Energy?
- Energy is the total amount of work done.
- Where, Power is the rate at which that work is done per unit of time.
- The SI unit of Energy is the Joule (J).
- The SI unit of power is the watt (W).
Key Relationship:
$$P = \frac{E}{t} \quad \text{and} \quad E = P \times t$$
Where,
- $P$ = Power
- $E$ = Energy Transferred
- $t$ = Time
How to Calculate Energy?
Steps to Calculate Energy:
1
Identify the term.
2
Apply the formula.
3
Calculate the energy.
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Solved Example
A machine uses 100 watts of power and runs for 5 seconds. How much energy does it use?
SOLUTION
1
Given:
- $P = 100$ watts
- $t = 5$ seconds
2
Using the formula:
$$E = P \times t$$
$$E = 100 \times 5 = 500$$
It used 500 joules of energy in 5 seconds.
Final Answer: 500 joules
Solved Example
A 60-watt bulb is turned on for 10 seconds. How much energy does it use?
SOLUTION
1
Identify the Term:
- $P = 60$ watts
- $t = 10$ seconds
2
Apply the formula (Putting the values in formula):
$$E = P \times t$$
3
Calculate the Energy:
$$E = 60 \times 10 = 600$$
It used 600 joules of energy in 10 seconds.
Final Answer: 600 joules
Solved Example
A car engine uses 10,000 joules of energy in 20 seconds. What is its power?
SOLUTION
1
Identify the Term:
- $E = 10,000$ joules
- $t = 20$ seconds
2
Apply the formula:
$$P = \frac{E}{t}$$
3
Calculate the Energy (Putting the values in formula):
$$P = \frac{10,000}{20} = 500$$
The Power of car engine is 500 watts.
Final Answer: 500 watts
Solved Example
A mobile charger uses 15 watts of power. How much energy will it use in 2 minutes?
SOLUTION
1
Identify the Term:
- $P = 15$ Watts
- $t = 2$ minutes ($2 \times 60$ seconds = $120$ seconds)
2
Apply the formula:
$$E = P \times t$$
3
Calculate the Energy (Putting the values in formula):
$$E = 15 \times 120 = 1800$$
It uses 1800 joules of energy in 2 minutes.
Final Answer: 1800 joules
Frequently Asked Questions
Energy is the ability to do work or cause change. It powers movement, heat, light, and machines.
The SI unit of Energy is the Joule (J).
- Kinetic Energy – motion
- Potential Energy – position or stored
- Thermal Energy – heat
- Energy = Total work done.
- Power = How fast energy is used.
No. According to the Law of Conservation of Energy, Energy can neither be created nor destroyed, only changed from one form to another.
- Renewable: Comes from natural sources that won’t run out (sunlight, wind, water).
- Non-renewable: Comes from sources that will eventually run out (coal, oil, gas).
