Is it correct to say: Applying Ohm's law to a diode or bulb filament?

Ohm's law holds only for ohmic conductors at constant temperature. Diodes, bulbs (hot filament) are non-ohmic.

Is it correct to say: Adding resistors in parallel like series?

In parallel, add reciprocals: 1/R_p = Σ 1/R_k. Equivalent is smaller than any branch.

Is it correct to say: Confusing kW with kWh?

kW is power (rate); kWh is energy (rate × time). Bills are in kWh.

Is it correct to say: Fuse placed in the neutral wire?

Fuse always goes in the LIVE wire so the appliance is disconnected during a fault.

Is it correct to say: Using V and I without conversion (mA vs A, mV vs V)?

SI units are A and V. Convert 100 mA = 0.1 A before plugging into V = IR.

Is it correct to say: Assuming current is used up in a bulb?

Current is the same before and after the bulb. Energy is used, not charge.

Effects of Electric Current

Ohm's law, resistance, heating and magnetic effects, electric power — Maharashtra SSC Science-1 Ch 4

📐 8 formulas✏️ 3 examples🎯 6 practice⚖️ 6 marks🏫 Maharashtra State Board📚 Class 10✓ 2025–26 syllabus

💡

Board Exam Tips

→Ohm's law + V–I graph is a definite 3-mark question every SSC paper.
→Series vs parallel: state one advantage and one disadvantage of each.
→Heating effect (H = I²Rt) numericals — practise units carefully (kWh vs J).
→Fleming's left-hand rule diagram must be labelled for full marks.
→Domestic wiring — live, neutral, earth colours and fuse position are asked as 2-mark question.

📊 Diagram

Simple circuit: battery, resistor and ammeter in series with voltmeter in parallel

📐 Formulas(8)

Electric Current

I = \frac{Q}{t}

Ohm's Law★ Board fav

V = I R

Symbol	Meaning
$V$	Potential difference (V)
$I$	Current (A)
$R$	Resistance (Ω)

Resistance and Resistivity

R = ρ \frac{L}{A}

Symbol	Meaning
$ρ$	Resistivity (Ω·m)
$L$	Length of conductor (m)
$A$	Cross-section area (m²)

Resistors in Series★ Board fav

R_{s} = R_{1} + R_{2} + R_{3} + \dots

Resistors in Parallel★ Board fav

\frac{1}{R _{p}} = \frac{1}{R _{1}} + \frac{1}{R _{2}} + \dots

Electric Power

P = V I = I^{2} R = \frac{V ^{2}}{R}

Joule's Law (Heat Produced)

H = I^{2} R t

Commercial Energy (kWh)

E (kWh) = \frac{P ( W ) \times t ( h )}{1000}

✏️ Solved Examples

1Solved Exampleeasy3 steps

A wire has resistance 10 Ω. A potential difference of 20 V is applied across it. Find the current.

Apply Ohm's law

I = \frac{V}{R}

2Solved Exampleboard4 steps

Two resistors of 6 Ω and 3 Ω are connected in parallel across a 12 V battery. Find (i) equivalent resistance, (ii) current through each and (iii) total power.

Parallel combination

\frac{1}{R _{p}} = \frac{1}{6} + \frac{1}{3} = \frac{1 + 2}{6} = \frac{1}{2}

3Solved ExampleHOTS3 steps

An electric heater rated 1500 W is used for 3 hours daily. Calculate the cost of energy consumed in 30 days at Rs. 4 per unit.

Daily energy consumption in kWh

E_{d a y} = \frac{P \times t}{1000} = \frac{1500 \times 3}{1000} = 4.5 kWh

⚠️ Traps & Common Mistakes

⚠️Common Mistakes6

1
Applying Ohm's law to a diode or bulb filament
✓Ohm's law holds only for ohmic conductors at constant temperature. Diodes, bulbs (hot filament) are non-ohmic.
2
Adding resistors in parallel like series
✓In parallel, add reciprocals: 1/R_p = Σ 1/R_k. Equivalent is smaller than any branch.
3
Confusing kW with kWh
✓kW is power (rate); kWh is energy (rate × time). Bills are in kWh.
4
Fuse placed in the neutral wire
✓Fuse always goes in the LIVE wire so the appliance is disconnected during a fault.
5
Using V and I without conversion (mA vs A, mV vs V)
✓SI units are A and V. Convert 100 mA = 0.1 A before plugging into V = IR.
6
Assuming current is used up in a bulb
✓Current is the same before and after the bulb. Energy is used, not charge.

🎯 Practice Yourself

🎯Practice Yourself6 questions

Q1
State Ohm's law. Draw the V–I graph for an ohmic conductor.
Q2
Two resistors of 5 Ω and 10 Ω are connected in series across a 15 V battery. Find the current.
Q3
A bulb draws 0.5 A on a 220 V supply. Find its resistance and power.
Q4
Convert 3.6×10⁶ J into kWh.
Q5
State one advantage of parallel connection over series in home wiring.
Q6
Calculate the heat produced in a 20 Ω resistor when 2 A current flows through it for 10 minutes.

📝 Notes

Effects of Electric Current — Maharashtra SSC

Chapter 4 of Science Part 1 focuses on the two main effects of current — heating and magnetic — after establishing Ohm's law and the resistor combinations. Unlike the CBSE Class 10 book (which splits electricity and magnetism into two chapters), Maharashtra packs both effects into one, so the answer paper must handle diagrams from both.

Ohm's law — assumptions

Ohm's law V = IR holds only when:

Temperature stays constant.
The conductor is metallic (ohmic).
Physical dimensions do not change.

If any of these change, V vs I is not a straight line.

Series and parallel — quick contrast

| Feature | Series | Parallel | |---|---|---| | Current | Same through all | Adds up | | Voltage | Adds up | Same across all | | Equivalent R | Larger than largest | Smaller than smallest | | Failure of one | Breaks circuit | Others continue |

Heating effect — Joule's law

Every conductor with resistance dissipates energy as heat when current flows. This is exploited in bulbs, heaters, irons and fuses.

Magnetic effect — quick facts

Oersted's experiment: current-carrying wire deflects a magnetic needle.
Right-hand thumb rule: thumb along current, curled fingers show magnetic field direction.
Solenoid acts like a bar magnet — used in electromagnets.
Fleming's left-hand rule: for the force on a current-carrying conductor in a magnetic field (motor rule).

Domestic wiring safety

Live (red/brown), neutral (black/blue), earth (green) — memorise the colour code.
Fuse and switch on live wire only.
Earthing protects from electric shock during insulation failure.

Board vs CBSE

Both boards teach the same physics, but Maharashtra SSC combines electricity and magnetism into one chapter and asks more everyday-life numericals (electricity bills, appliance ratings). CBSE separates them and demands cleaner circuit diagrams.