# Electricity and Magnetism - Grade 10 (SEE) Physics
## Complete Topper Level Notes - NEB Curriculum 2080

---

## 🎯 Chapter Overview
**Chapter 6: Electricity and Magnetism** is one of the most important chapters in Grade 10 Physics for SEE examination. This chapter covers fundamental concepts of electric current, magnetic fields, electromagnetic induction, and their practical applications.

**Weightage:** 15-20 marks in SEE examination
**Time Required:** 25-30 periods

---

## 📚 Learning Objectives
After studying this chapter, students will be able to:
- Understand electric current and its effects
- Explain magnetic fields and their properties
- Analyze electromagnetic induction phenomena
- Apply concepts in practical devices like motors, generators, and transformers

---

## ⚡ 1. ELECTRIC CURRENT

### 1.1 Definition
Electric current is the flow of electric charges (electrons) through a conductor per unit time.

**Formula:** 
```
I = Q/t
Where: I = Current (Ampere), Q = Charge (Coulomb), t = Time (Second)
```

**SI Unit:** Ampere (A)
- 1 Ampere = 1 Coulomb/1 Second
- 1 mA = 10⁻³ A
- 1 μA = 10⁻⁶ A

### 1.2 Types of Current

#### A. Direct Current (DC)
- Current flows in one direction only
- Constant magnitude and direction
- Sources: Battery, DC generator, solar cells
- Used in: Electronic devices, mobile phones, laptops

#### B. Alternating Current (AC)  
- Current changes direction periodically
- Magnitude and direction vary sinusoidally
- Frequency in Nepal: 50 Hz (changes direction 100 times per second)
- Sources: AC generator, power stations
- Used in: Household appliances, industrial equipment

### 1.3 Effects of Electric Current

#### 1. Heating Effect
- When current passes through a conductor, it heats up
- Electrical energy converts to heat energy
- **Applications:** Electric heater, iron, toaster, bulb filament
- **Formula:** H = I²Rt (Joule's Law)

#### 2. Magnetic Effect
- Current-carrying conductor behaves like a magnet
- Creates magnetic field around the conductor
- **Applications:** Electromagnet, electric bell, motor, generator

#### 3. Chemical Effect
- Current can cause chemical changes in electrolytes
- **Applications:** Electroplating, electrolysis, battery charging

---

## 🧲 2. MAGNETISM

### 2.1 Magnetic Field
The space around a magnet where its magnetic influence can be felt.

**Properties of Magnetic Field Lines:**
- They form closed loops
- Never intersect each other
- Density indicates field strength
- Direction: North to South (outside magnet)

**SI Unit:** Tesla (T) or Weber/m²
- 1 Tesla = 10⁴ Gauss

### 2.2 Magnetic Field due to Current

#### Oersted's Discovery (1820)
Danish physicist Hans Christian Oersted discovered that electric current produces magnetic field.

#### Right Hand Thumb Rule
If the thumb of right hand points in the direction of current, then the curled fingers show the direction of magnetic field lines.

#### Magnetic Field Formulas

**1. Straight Current-Carrying Conductor:**
```
B = (μ₀I)/(2πr)
Where: μ₀ = 4π × 10⁻⁷ T⋅m/A (permeability of free space)
       I = Current, r = distance from conductor
```

**2. Circular Current-Carrying Coil (at center):**
```
B = (μ₀I)/(2r)
Where: r = radius of coil
```

**3. Solenoid (inside):**
```
B = μ₀nI
Where: n = number of turns per unit length (N/l)
```

### 2.3 Force on Current-Carrying Conductor

When a current-carrying conductor is placed in a magnetic field, it experiences a force.

**Formula:**
```
F = BIL sin θ
Where: B = Magnetic field, I = Current, L = Length of conductor
       θ = angle between current and magnetic field
```

**Fleming's Left Hand Rule:**
- **Thumb:** Direction of force (motion)
- **First finger:** Direction of magnetic field
- **Middle finger:** Direction of current

---

## 🔄 3. ELECTROMAGNETIC INDUCTION

### 3.1 Faraday's Law of Electromagnetic Induction

**Statement:** "Whenever there is a change in magnetic flux linked with a closed circuit, an EMF is induced in the circuit."

**Mathematical Form:**
```
ε = -dΦ/dt = -N(dΦ/dt)
Where: ε = induced EMF, Φ = magnetic flux, N = number of turns
```

**Magnetic Flux:** Φ = BA cos θ
- B = magnetic field, A = area, θ = angle between B and area normal

### 3.2 Lenz's Law
"The direction of induced current is such that it opposes the change that produced it."

### 3.3 Fleming's Right Hand Rule
Used to find direction of induced current:
- **Thumb:** Direction of motion of conductor
- **First finger:** Direction of magnetic field  
- **Middle finger:** Direction of induced current

### 3.4 Methods to Increase Induced EMF
1. Increase the rate of change of magnetic flux
2. Increase the number of turns in the coil
3. Use stronger magnets
4. Move conductor faster through magnetic field

---

## ⚙️ 4. PRACTICAL APPLICATIONS

### 4.1 Electric Motor
**Principle:** Force on current-carrying conductor in magnetic field (Fleming's Left Hand Rule)

**Function:** Converts electrical energy into mechanical energy

**Construction:**
- Armature (rotating coil)
- Field magnets
- Commutator
- Carbon brushes

**Applications:** Fans, washing machines, mixers, electric vehicles

### 4.2 Electric Generator (Dynamo)
**Principle:** Electromagnetic induction (Fleming's Right Hand Rule)

**Function:** Converts mechanical energy into electrical energy

**EMF Equation:**
```
E = (PΦNz)/(60A)
Where: P = number of poles, Φ = flux per pole
       N = speed (rpm), z = total conductors, A = parallel paths
```

**Types:**
- **DC Generator:** Produces direct current
- **AC Generator:** Produces alternating current

### 4.3 Transformer
**Principle:** Mutual induction between two coils

**Function:** Changes AC voltage level (step-up or step-down)

**Transformer Equation:**
```
Vp/Vs = Np/Ns = Is/Ip
Where: p = primary, s = secondary
       V = voltage, N = turns, I = current
```

**Types:**
- **Step-up Transformer:** Ns > Np (increases voltage)
- **Step-down Transformer:** Ns < Np (decreases voltage)

**Applications:**
- Power transmission
- Mobile chargers
- Welding transformers
- Distribution systems

### 4.4 Electric Bell
**Working:**
1. When switch is pressed, current flows through electromagnet
2. Electromagnet attracts iron armature
3. Hammer strikes the gong producing sound
4. Circuit breaks, electromagnet loses magnetism
5. Spring pulls armature back, completing circuit again
6. Process repeats rapidly creating continuous ringing

---

## 🔌 5. HOUSEHOLD ELECTRICITY

### 5.1 Electric Wiring
**Three-wire System:**
- **Live Wire (Red/Brown):** Carries current to appliance
- **Neutral Wire (Black/Blue):** Completes the circuit
- **Earth Wire (Green):** Safety wire for metal bodies

### 5.2 Safety Devices

#### Fuse
- Thin wire that melts when excess current flows
- Connected in series with live wire
- **Rating:** Should be slightly higher than normal current

#### Circuit Breaker
- Electromagnetic switch that opens circuit during overload
- Can be reset after fault is cleared
- More reliable than fuse

#### Earth Wire
- Connects metal body of appliances to ground
- Provides path for leakage current
- Prevents electric shock

### 5.3 Electric Power and Energy

**Power:** P = VI = I²R = V²/R (Watts)

**Energy:** E = Pt (Joules)

**Commercial Unit:** kWh (kilowatt-hour)
- 1 kWh = 3.6 × 10⁶ J
- Used for electricity billing

---

## 📊 6. IMPORTANT FORMULAS SUMMARY

### Current and Resistance
- Current: I = Q/t
- Ohm's Law: V = IR
- Power: P = VI = I²R = V²/R
- Energy: E = Pt

### Magnetic Field
- Straight conductor: B = μ₀I/(2πr)
- Circular coil: B = μ₀I/(2r)
- Solenoid: B = μ₀nI
- Force on conductor: F = BIL sin θ

### Electromagnetic Induction
- Faraday's Law: ε = -N(dΦ/dt)
- Magnetic flux: Φ = BA cos θ
- Generator EMF: E = (PΦNz)/(60A)
- Transformer: Vp/Vs = Np/Ns

### Constants
- μ₀ = 4π × 10⁻⁷ T⋅m/A
- 1 Tesla = 10⁴ Gauss
- 1 kWh = 3.6 × 10⁶ J

---

## 🎯 7. EXAM IMPORTANT TOPICS

### Very Important (Must Know)
1. Faraday's laws of electromagnetic induction
2. Fleming's left and right hand rules
3. Working principle of motor and generator
4. Transformer principle and equation
5. AC vs DC comparison
6. Magnetic field due to current-carrying conductors

### Important
1. Electric bell working
2. Safety devices in household wiring
3. kWh and its relation to joule
4. Lenz's law
5. Methods to increase induced EMF
6. Types of transformers

### Moderate
1. Oersted's experiment
2. Properties of magnetic field lines
3. Electric power calculations
4. Factors affecting electromagnet strength

---

## 💡 8. NUMERICAL PROBLEMS PRACTICE

### Type 1: Current and Power
**Q1:** A device draws 5A current for 2 hours. Calculate the charge flow.
**Solution:** Q = It = 5 × 2 × 3600 = 36,000 C

### Type 2: Magnetic Field
**Q2:** Calculate magnetic field at 10 cm from a wire carrying 2A current.
**Solution:** B = μ₀I/(2πr) = (4π×10⁻⁷×2)/(2π×0.1) = 4×10⁻⁶ T

### Type 3: Transformer
**Q3:** A transformer has 1000 primary turns and 100 secondary turns. If primary voltage is 220V, find secondary voltage.
**Solution:** Vs = Vp × Ns/Np = 220 × 100/1000 = 22V

---

## 🔬 9. PRACTICAL EXPERIMENTS

### Experiment 1: Oersted's Experiment
**Aim:** To show magnetic effect of electric current
**Procedure:**
1. Place a compass needle near a current-carrying wire
2. Switch on current and observe needle deflection
3. Reverse current direction and observe

### Experiment 2: Electromagnetic Induction
**Aim:** To demonstrate Faraday's law
**Procedure:**
1. Connect a coil to galvanometer
2. Move a magnet towards/away from coil
3. Observe galvanometer deflection

---

## 📝 10. EXAM PREPARATION TIPS

### For Theory Questions
1. **Definitions:** Learn exact definitions with units
2. **Laws:** State laws with mathematical expressions
3. **Principles:** Understand working principles of devices
4. **Diagrams:** Practice neat labeled diagrams

### For Numerical Problems
1. **Formulas:** Memorize all important formulas
2. **Units:** Always check unit consistency
3. **Steps:** Show all calculation steps clearly
4. **Practice:** Solve various types of problems

### Common Mistakes to Avoid
1. Confusing Fleming's left and right hand rules
2. Wrong transformer equation application
3. Mixing up AC and DC properties
4. Incorrect magnetic field direction

---

## 🏆 11. PREVIOUS YEAR SEE QUESTIONS PATTERN

### Theory Questions (2-3 marks each)
- Define electromagnetic induction
- State Faraday's laws
- Explain working of electric motor
- Compare AC and DC
- Describe safety measures in household wiring

### Numerical Questions (3-4 marks each)
- Transformer calculations
- Magnetic field calculations
- Power and energy problems
- Current and charge calculations

### Long Questions (5-6 marks)
- Working principle of generator with diagram
- Complete explanation of transformer
- Electric bell mechanism with diagram

---

## 📖 12. ADDITIONAL STUDY RESOURCES

### Reference Books
1. NEB Textbook (Class 10 Science)
2. Khullakitab Notes
3. Readersnepal Guide
4. Local guide books

### Online Resources
1. Khan Academy Physics
2. YouTube educational channels
3. PhET simulations
4. Educational websites

---

## ✅ 13. CHAPTER CHECKLIST

**Before SEE Exam, ensure you can:**
- [ ] Explain all three effects of electric current
- [ ] Apply Fleming's rules correctly
- [ ] Solve transformer numerical problems
- [ ] Draw and explain motor/generator diagrams  
- [ ] Calculate magnetic fields using formulas
- [ ] Describe household electrical safety
- [ ] Compare different types of current
- [ ] Explain electromagnetic induction completely

---

## 🎊 CONCLUSION

Electricity and Magnetism is a scoring chapter if concepts are clear. Focus on understanding principles rather than memorizing. Practice numerical problems regularly and draw neat diagrams. This chapter forms the foundation for advanced physics topics in higher classes.

**Remember:** Physics is not about memorizing formulas but understanding the beauty of nature's laws!

---

*This note is prepared according to NEB curriculum 2080 for SEE examination. Best wishes for your preparation!*

**📞 Need Help?** Practice more problems and refer to your textbook for additional examples.

---