Rahul DevashishCoursePhysics Electricity

2 Sept 2025·6 min read·

Electricity

Electricity is the flow of electric charge (electrons) through a conductor.
It is a vital form of energy used in homes, industries, agriculture, and digital systems.
In Bihar, electricity access has grown through schemes like Saubhagya, PM-KUSUM, and solar energy initiatives under BREDA.

Electric Current and Charge

Electric Current (I) = Flow of electric charge
Formula: I = Q / t
- I: Current (Ampere)
- Q: Charge (Coulomb)
- t: Time (seconds)
SI Unit of Current = Ampere (A)
SI Unit of Charge = Coulomb (C)

📝 PYQ (BPSC): SI unit of electric current? → Ampere

Electric Potential and Potential Difference

Electric Potential: Work done in bringing unit charge
Potential Difference (V) = Work/Charge
- Unit: Volt (V)
1 Volt = 1 Joule / 1 Coulomb

📝 Expected MCQ: Unit of potential difference? → Volt

Ohm's Law

States: V = I × R
- V: Voltage, I: Current, R: Resistance
Used in designing circuits
Graph of V vs I is a straight line for ohmic conductors

📝 PYQ (BPSC): Ohm’s Law gives the relation between? → V, I, R

Resistance

Opposition to flow of current
Unit: Ohm (Ω)
Factors affecting resistance:
- Length ↑ → Resistance ↑
- Area ↑ → Resistance ↓
- Material & temperature also matter

Effects of Electric Current

1. Heating Effect

Heat = H = I²Rt
Used in: electric heaters, fuses, bulbs, toasters

📝 PYQ: Which effect is used in electric heaters? → Heating effect of current

2. Magnetic Effect

Discovered by Oersted
Basis of electromagnets, electric bells, motors

3. Chemical Effect

Seen in electrolysis
Applications: Electroplating, Battery charging

Electric Power and Energy

Power: P = V × I
- Unit: Watt (W)
- 1 Kilowatt (kW) = 1000 W
Energy: E = P × t
- Commercial unit: kWh (unit in electric bill)

📝 Expected MCQ: Unit used in electricity bills? → kWh
📝 Expected MCQ: 1 kWh = ? → 3.6 × 10⁶ J

Circuit Symbols and Components

Battery = Two or more cells
Resistor = Limits current
Switch = Opens or closes circuit
Ammeter = Measures current (in series)
Voltmeter = Measures voltage (in parallel)
Fuse = Prevents overcurrent

Series and Parallel Circuits

Series:

Same current, different voltage
Total Resistance = R₁ + R₂ + R₃...
Used in fuse circuits

Parallel:

Same voltage, current splits
Total Resistance = 1/R = 1/R₁ + 1/R₂...
Used in home wiring → safer, more efficient

📝 Expected MCQ: In homes, appliances are connected in? → Parallel

Bihar-Specific Applications

PM-KUSUM: Solar-powered agricultural pumps
Saubhagya Yojana: Universal electrification in Bihar
BREDA: Solar grids in off-grid rural areas
Smart meters installation for power efficiency
Electric fencing, solar street lights in border districts
Schools: Use of solar inverters, EduSat power

PYQs + Expected MCQs

📝 PYQ (BPSC): Ohm’s Law gives relation between? → V, I, R
📝 PYQ: SI unit of electric current? → Ampere
📝 PYQ: Which effect is used in electric heater? → Heating effect
📝 Expected MCQ: Commercial unit of electrical energy? → kWh
📝 Expected MCQ: Circuit in homes is? → Parallel
📝 Expected MCQ: Resistance unit? → Ohm (Ω)
📝 Expected MCQ: What happens if resistance increases? → Current decreases
📝 Expected MCQ: Who discovered magnetic effect of current? → Oersted

Quick Revision Points

Current = Q / t, Unit = Ampere
Charge unit = Coulomb
Voltage = Work / Charge, Unit = Volt
Ohm’s Law: V = I × R
Resistance unit = Ohm (Ω)
Power = V × I, Energy = P × t
1 kWh = 3.6 × 10⁶ J
Heating Effect → in toasters, heaters
Magnetic Effect → electric motor, bell
Chemical Effect → electroplating
Bihar: Solar irrigation, Saubhagya, BREDA grid

Conductivity is the property of a material to allow the flow of electric current (electrical conductivity) or heat (thermal conductivity).
It depends on the availability and mobility of charge carriers (electrons/ions) for electrical conductivity and on particle vibration/energy transfer for thermal conductivity.
In Bihar, conductivity studies are used in soil testing for agriculture, groundwater detection, and industrial quality control.

Types of Conductivity

Electrical Conductivity
- Measure of a material’s ability to conduct electric current
- Unit: Siemens per meter (S/m)
- Inverse of resistivity (σ = 1/ρ)
- Metals → High, Non-metals → Low
Thermal Conductivity
- Measure of a material’s ability to transfer heat
- Unit: Watt per meter per Kelvin (W/m·K)
- Metals like copper, silver → Very high; wood, plastic → Very low
Ionic Conductivity
- Movement of ions in solution or solid electrolyte
- Important in electrolysis, batteries, fuel cells

Factors Affecting Conductivity

Electrical:
- Temperature (↑ temp → ↓ conductivity in metals, ↑ in semiconductors)
- Nature of material (free electron density)
- Impurities and alloying
Thermal:
- Material structure (crystalline > amorphous)
- Temperature (varies for metals/non-metals)
- Moisture content in solids/liquids

Applications & Relevance

Electrical: Power transmission, electronics, wiring
Thermal: Cookware (copper/aluminium), heat sinks in electronics
Industrial: Quality testing of water, soil conductivity for agriculture
Bihar Context:
- Soil conductivity meters for fertilizer recommendations
- Groundwater mapping via electrical resistivity surveys in drought-prone districts
- Industrial applications in sugar mills and thermal power plants

Conductivity in Different Materials (Approximate Order)

Highest electrical conductivity: Silver > Copper > Gold > Aluminium
Lowest: Rubber, glass, plastic (insulators)
High thermal conductivity: Diamond, silver, copper
Low thermal conductivity: Wood, styrofoam, wool

Historical/Conceptual Background

Georg Ohm (1827) → Related conductivity to resistance (Ohm’s Law)
Fourier’s Law → Governs thermal conductivity
Concept central to the development of telegraph, electricity distribution, and modern electronics

Bihar Applications Examples

BREDA solar power projects use high-conductivity copper wiring
Patna University geology dept. uses conductivity surveys for groundwater
Krishi Vigyan Kendras test soil conductivity for crop planning

PYQs + Expected MCQs

📝 PYQ (BPSC 2011): Which metal has the highest electrical conductivity? → Silver
📝 Expected MCQ: Unit of electrical conductivity? → Siemens per meter (S/m)
📝 Expected MCQ: Which factor decreases electrical conductivity of metals? → Increase in temperature
📝 Expected MCQ: Good thermal conductor? → Copper
📝 Expected MCQ: What type of conductivity is used in electrolysis? → Ionic conductivity

Quick Revision Points

Conductivity = Ease of flow of current/heat
Electrical unit: S/m, Thermal unit: W/m·K
Electrical conductivity ∝ free electron density
Metals = Good conductors; non-metals = Insulators
Silver = Best electrical conductor, Diamond = Best thermal conductor
In metals: ↑ temp → ↓ electrical conductivity
Bihar: Soil & water conductivity used in agriculture and hydrology

Sources Used

NCERT Class 10 Physics
Lucent GK – Physics
Ghatna Chakra Science PYQs
Drishti Bihar Science Notes
Eduteria Bihar Science Compendium
Bihar Agriculture Dept. Reports

Sources Used

NCERT Class 9–10 Science
Lucent GK – Physics Section
Drishti Science & Technology Quick Book
Ghatna Chakra BPSC PYQs
EduTeria BPSC Science Set
BREDA – Bihar Renewable Energy Reports
Bihar Energy Department Schemes (Saubhagya, Kusum)