Electric Current and Ohm's Law
NCERT Class 10 • Science • Chapter "Electricity"
Electric Current and Ohm's Law
Electric current is the rate of flow of electric charge through a conductor. Charge flows only when there is a potential difference across the two ends of the conductor, which a cell or battery provides, and the circuit must be complete for the flow to continue.
Current, Potential Difference and Resistance
- Current is charge divided by time, and its SI unit is the ampere.
- Conventional current is taken to flow from the positive to the negative terminal, opposite to the direction of electron flow.
- Potential difference is the work done to move a unit charge between two points, measured in volt.
- Current is measured with an ammeter connected in series and potential difference with a voltmeter connected in parallel.
- Ohm's law states that at constant temperature, current through a conductor is directly proportional to the potential difference across it.
- From it comes V = IR, where R is the resistance, measured in ohm.
- Resistance opposes the flow of current and converts electrical energy into heat.
Factors and Combinations
- Resistance is directly proportional to length and inversely proportional to the area of cross section of the conductor.
- It also depends on the material, described by its resistivity, and it rises with temperature in metals.
- A thick short wire of a good conductor therefore has low resistance.
- In series, the same current flows through all resistors and the total resistance is the sum of the individual resistances.
- In parallel, the potential difference is the same across all and the total resistance is less than the smallest individual resistance.
- Household appliances are connected in parallel so each works at full voltage and can be switched independently.
- A rheostat is a variable resistor used to change the current in a circuit without changing the source.
| Quantity | Symbol | Unit |
|---|---|---|
| Current | I | ampere |
| Potential difference | V | volt |
| Resistance | R | ohm |
Ohm's law — at constant temperature, the current through a conductor is directly proportional to the potential difference across its ends.
Hindi me samjhein
श्रेणी क्रम में कुल प्रतिरोध जुड़ जाता है, इसलिए वह बढ़ता है। समांतर क्रम में कुल प्रतिरोध सबसे छोटे प्रतिरोध से भी कम हो जाता है, इसीलिए घरों में समांतर क्रम लगाया जाता है।
Exam me kaise aata hai
- The SI unit of resistance is the — ohm
- An ammeter is connected in — series
- A voltmeter is connected in — parallel
- Household appliances are connected in — parallel
UPSC/State PSC ke liye
- Appliances are wired in parallel so that each receives the full supply voltage and one failing device does not break the circuit for the rest.
- Resistance rises with temperature in metals because increased vibration of atoms obstructs the drift of electrons.
Yahan confuse hote hain
✗ An ammeter is connected in parallel | An ammeter goes in series; a voltmeter in parallel | ✓
✗ Total resistance in parallel is larger | In parallel it is less than the smallest resistance | ✓
✗ Conventional current is the direction of electron flow | Conventional current is opposite to electron flow | ✓
Ek nazar me
- Current is charge per unit time in ampere; potential difference is in volt.
- Ohm's law gives V = IR with resistance in ohm.
- Resistance rises with length and falls with thickness.
- Series adds resistance; parallel lowers it, which is why homes use parallel wiring.