Electricity, Light, Sound
Complete SSC GD Syllabus Coverage
Electricity, light, and sound are core physics topics asked frequently in SSC GD, SSC CGL, Railways, and state-level exams. This article explains all concepts in simple, exam-oriented language.
1. Electricity
Electricity is the flow of electric charge through a conductor.
Simple Definition: Electricity is the movement of electrons in a wire.
2. Electric Charge
Types:
- Positive charge
- Negative charge
Like charges repel; unlike charges attract.
SI Unit:
Coulomb (C)
3. Electric Current
Electric current is the rate of flow of electric charge.
Formula:
Current (I) = Charge (Q) / Time (t)
Details:
- SI Unit: Ampere (A)
- Device to measure current: Ammeter
- Connected in series
4. Voltage or Potential Difference
Voltage is the force that pushes current through a circuit.
Details:
- SI Unit: Volt (V)
- Device: Voltmeter
- Connected in parallel
5. Resistance
Resistance opposes the flow of electric current.
SI Unit: Ohm (Ω)
Ohm's Law:
V = I × R
(Voltage = Current × Resistance)
6. Conductors and Insulators
Conductors
Allow electricity to pass through.
Examples:
- Copper
- Aluminium
- Iron
- Water
Insulators
Do not allow electricity to pass through.
Examples:
- Plastic
- Rubber
- Wood
- Glass
7. Electric Power
Formula:
Power = Voltage × Current
SI Unit: Watt (W)
Important Conversions:
- 1 kilowatt (kW) = 1000 W
- 1 unit of electricity = 1 kWh
8. Heating Effect of Current
Current produces heat when it flows through a wire.
Applications:
- Electric iron
- Electric heater
- Geyser
- Bulbs
9. Magnetic Effect of Current
Electric current produces a magnetic field.
Applications:
- Electric bell
- Electric motor
- Transformers
10. Electric Cell and Battery
Electric cell converts chemical energy into electrical energy.
Types:
- Dry cell: used in torch, remote
- Battery: combination of cells
11. Series and Parallel Circuits
Series
- Only one path for current
- If one component fails, circuit breaks
Parallel
- Multiple paths for current
- Used in household wiring
12. AC and DC Current
AC (Alternating Current)
- Changes direction periodically
- Used in homes
- Frequency in India: 50 Hz
DC (Direct Current)
- Flows in one direction
- Used in batteries
13. Fuse
A fuse protects circuit from overheating.
Construction:
- Made of a low melting point metal (tin-lead alloy)
- Melts when current is high
14. Magnetism Basics
- Magnet has two poles: North and South
- Like poles repel; unlike poles attract
- Earth behaves like a big magnet
15. Electromagnet
Magnet formed by passing current through a coil.
Applications:
- Cranes
- Motors
- Relays
Light
16. What is Light?
Light is a form of energy that enables us to see objects.
Properties:
- Speed of light in vacuum: 3 × 10⁸ m/s
- Light travels in a straight line
17. Reflection of Light
Bouncing back of light from a surface.
Laws of Reflection:
- Incident ray = Reflected ray
- Angle of incidence = Angle of reflection
Applications: Mirrors, periscopes
18. Types of Mirrors
Plane Mirror
- Forms same-sized image
Concave Mirror
- Curved inward
- Used in shaving mirrors, headlights
Convex Mirror
- Curved outward
- Used in vehicles' rearview mirrors
19. Refraction of Light
Bending of light when it passes from one medium to another.
Examples:
- Straw appearing bent in a glass
- Twinkling of stars
20. Lenses
Convex Lens
- Thicker in middle
- Converges light
- Used in magnifying glass, cameras
Concave Lens
- Thinner in middle
- Diverges light
- Used in spectacles for short-sightedness
21. Dispersion of Light
Splitting of white light into seven colors. This forms a rainbow.
Seven Colors (VIBGYOR):
- Violet
- Indigo
- Blue
- Green
- Yellow
- Orange
- Red
22. Human Eye (Basic)
Structure:
- Lens: Convex
- Image forms: On retina
Defects:
- Myopia (short-sightedness) – concave lens
- Hypermetropia (long-sightedness) – convex lens
Sound
23. What is Sound?
Sound is a form of energy produced by vibrations.
Travel Characteristics:
- Travels fastest in solids
- Slowest in gases
- Cannot travel in vacuum
24. Frequency, Amplitude, Wavelength
Frequency
- Number of vibrations per second
- Unit: Hertz (Hz)
Amplitude
- Maximum displacement of vibration
- Determines loudness
Wavelength
- Distance between two crests or troughs
25. Speed of Sound
Speed of sound in air: 330 m/s (approx)
Speed in Different Media:
- Faster in liquids
- Fastest in solids
26. Types of Sounds
Audible Sound
20 Hz to 20,000 Hz
Infrasonic
below 20 Hz
Ultrasonic
above 20,000 Hz
Bats and dolphins use ultrasonic waves.
27. Echo
Reflection of sound.
Echo can be heard if the reflecting surface is at least 17 meters away.
28. Noise and Music
Noise
unpleasant sound
Music
pleasant sound
29. SONAR
Full Form:
Sound Navigation and Ranging
Application:
Uses ultrasonic waves to measure depth in oceans.
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