Electric Current, Power, Energy and Voltage
Complete Notes for Competitive Examinations
By Home Academy
1. Introduction
Electricity is one of the most important branches of physics and is widely used in homes, industries, communication systems, transportation, and technology. Questions related to electric current, voltage, power, and electrical energy are frequently asked in SSC, JKSSB, Railway, Banking, NEET, UPSC, and State-level examinations.
2. Electric Current
Definition
Electric current is the rate of flow of electric charge through a conductor.
Formula
I = \frac{Q}{t}
Where:
I = Electric current
Q = Electric charget = Time
SI Unit of Current
| Quantity | SI Unit | Symbol |
|---|---|---|
| Electric Current | Ampere | A |
Important Points About Current
Current flows from higher potential to lower potential.
Conventional current flows from positive to negative terminal.Electron flow is opposite to current direction.
Electric current is measured using an ammeter.
Ammeter is connected in series.
Types of Electric Current
| Type | Description |
|---|---|
| Direct Current (DC) | Flows in one direction |
| Alternating Current (AC) | Changes direction periodically |
Examples
Battery supplies DC current.
Household electricity is AC.
3. Electric Voltage
Definition
Voltage is the potential difference between two points in a circuit.
It is the work done to move a unit positive charge.
Formula
V = \frac{W}{Q}
Where:
V = Voltage
W = Work doneQ = Charge
SI Unit of Voltage
| Quantity | SI Unit | Symbol |
|---|---|---|
| Voltage | Volt | V |
Important Points About Voltage
Voltage is measured using a voltmeter.
Voltmeter is connected in parallel.Higher voltage means greater electrical push.
4. Electric Power
Definition
Electric power is the rate at which electrical energy is consumed or produced.
Formula
P = VI
Where:
P = Power
V = VoltageI = Current
Other Power Formulas
P = I^2R
P = \frac{V^2}{R}
SI Unit of Power
| Quantity | SI Unit | Symbol |
|---|---|---|
| Power | Watt | W |
Important Points About Power
1 kilowatt = 1000 watts
Electric bulbs and appliances are rated in watts.Greater power means more energy consumption.
5. Electrical Energy
Definition
Electrical energy is the total electrical work done or energy consumed.
Formula
E = Pt
Where:
E = Energy
P = Powert = Time
Commercial Unit of Energy
| Unit | Meaning |
|---|---|
| 1 kilowatt-hour (kWh) | Energy consumed by 1000 W in 1 hour |
1 kWh = 3.6 × 10⁶ joules
Important Points About Electrical Energy
Electricity bills are based on kWh.
Energy meter measures electrical energy.Higher appliance usage increases energy consumption.
6. Ohm’s Law
Statement
At constant temperature, current flowing through a conductor is directly proportional to voltage.
Formula
genui{"math_block_widget_always_prefetch_v2":{"content":"V = IR"}}
Where:
V = Voltage
I = CurrentR = Resistance
SI Unit of Resistance
| Quantity | SI Unit |
|---|---|
| Resistance | Ohm (Ω) |
7. Relationship Between Current, Voltage and Resistance
| Quantity Increases | Effect |
|---|---|
| Voltage increases | Current increases |
| Resistance increases | Current decreases |
8. Electrical Instruments
| Instrument | Function | Connection |
|---|---|---|
| Ammeter | Measures current | Series |
| Voltmeter | Measures voltage | Parallel |
| Energy Meter | Measures energy | Household supply |
9. Differences
Current vs Voltage
| Current | Voltage |
|---|---|
| Flow of charge | Potential difference |
| Measured in ampere | Measured in volt |
| Measured by ammeter | Measured by voltmeter |
Power vs Energy
| Power | Energy |
|---|---|
| Rate of energy use | Total energy consumed |
| Unit = Watt | Unit = Joule/kWh |
10. Applications in Daily Life
| Device | Use |
|---|---|
| Electric bulb | Produces light |
| Fan | Produces motion |
| Heater | Produces heat |
| Refrigerator | Cooling |
| Mobile charger | Charging battery |
11. Important Exam Points
SI unit of current = Ampere
SI unit of voltage = VoltSI unit of power = Watt
SI unit of energy = Joule
Commercial unit = kWh
Ammeter connected in series
Voltmeter connected in parallel
Household electricity is AC
Battery supplies DC
12. Frequently Asked MCQs
1. SI unit of electric current is:
A. Volt
B. Watt
C. Ampere
D. Ohm
✅ Answer: C
2. Instrument used to measure voltage:
A. Ammeter
B. Galvanometer
C. Voltmeter
D. Thermometer
✅ Answer: C
3. Commercial unit of electrical energy is:
A. Joule
B. Newton
C. kWh
D. Watt
✅ Answer: C
4. Power is measured in:
A. Joule
B. Watt
C. Volt
D. Ampere
✅ Answer: B
5. According to Ohm’s law:
A. V = IR
B. P = IR
C. E = IV
D. R = VI
✅ Answer: A
6. Ammeter is connected in:
A. Parallel
B. Series
C. Diagonal
D. None
✅ Answer: B
7. Household electricity is:
A. DC
B. AC
C. Static electricity
D. Solar current
✅ Answer: B
13. Statement-Based Questions
Question 1
Consider the following statements:
Electric current is measured in ampere.
Voltmeter is connected in series.
Household supply is AC.
A. Only 1 and 2
B. Only 1 and 3
C. Only 2 and 3
D. 1, 2 and 3
✅ Answer: B
Question 2
Which of the following statements are correct?
Power is the rate of energy consumption.
Electrical energy is measured commercially in kWh.
Ammeter has high resistance.
A. Only 1 and 2
B. Only 2 and 3
C. Only 1 and 3
D. 1, 2 and 3
✅ Answer: A
Question 3
Consider the following:
Battery supplies DC current.
Current flows from higher potential to lower potential.
Voltmeter is connected in parallel.
A. Only 1 and 2
B. Only 2 and 3
C. 1, 2 and 3
D. Only 1 and 3
✅ Answer: C
14. Assertion–Reason Questions
Assertion (A)
Voltmeter is connected in parallel.
Reason (R)
Voltmeter measures potential difference across a component.
A. Both A and R are true and R explains A
B. Both true but R not explanation
C. A true, R false
D. A false, R true
✅ Answer: A
Assertion (A)
Current decreases when resistance increases.
Reason (R)
According to Ohm’s law, current is inversely proportional to resistance.
A. Both A and R are true and R explains A
B. Both true but R not explanation
C. A true, R false
D. A false, R true
✅ Answer: A
15. One-Liner Revision
| Question | Answer |
|---|---|
| SI unit of current | Ampere |
| SI unit of voltage | Volt |
| SI unit of power | Watt |
| Commercial unit of energy | kWh |
| Formula of power | P = VI |
| Formula of energy | E = Pt |
| Instrument for current | Ammeter |
| Instrument for voltage | Voltmeter |
16. Numerical Example
Example
A bulb operates at:
Voltage = 220 V
Current = 2 A
Find power.
Solution
P = VI
P = 220 × 2 = 440 W
✅ Power = 440 watt
Conclusion
Electric current, voltage, power, and electrical energy are fundamental concepts of electricity and electronics. Understanding formulas, SI units, instruments, Ohm’s law, and practical applications is extremely important for competitive examinations and everyday life.
Prepared By Home Academy