Important points of sslc physics chapter 1


Electric iron – electrical energy is converted into heat energy

  • • Electric fan – electrical energy is converted into mechanical energy
  • • Electromagnet – electrical energy is converted into magnetic energy
  • • Electric heater – electrical energy is converted into heat energy
  • • Storage battery – electrical energy is converted into chemical energy.
    (while charging)
  • • Induction cooker – electrical energy is converted into heat energy
  • • Mixie – electrical energy is converted into mechanical energy

  • Heating Effect of Electric Current
    • Electric iron, electric heater, electric bulb etc. are the appliances working on the heating effect of electricity.
  • Two small pieces of thin copper wire and nichrome wire of nearly equal length and thickness, then the resistance of the nichrome wire is greater than that of copper wire.

• Copper wire and nichrome wire are connected in series, then the current
passing through them are same.

• The nichrome wire becomes red hot while passing electricity through the
circuit since resistance of nichrome is more.
Resistivity of nichrome is more than that of copper

If the ammeter shows a current I ampere on applying a potential difference
V across the resistor of resistance

Unit – Ampere (A)

The potential difference between two points will be one volt if one joule
of work is done in moving one coulomb of charge from one point to the
other. • Unit – Volt (V)

Joule’s Law:
•The heat generated (H) in a current carrying conductor is directly proportional to the product of the square of the current (I) in the conductor, the resistance of the conductor (R) and the time (t) of flow of
H. Vt
I – Current, R- Resistance, V – Voltage, t – Time,
P-Power, H – heat

The factors affecting the heat produced
1. Electric current 2. Resistance of the conductor 3. Time of flow of electric current

Series Connection:
When a circuit is completed by connecting the resistors one after the other,
it is called series connection.Effective resistance is the sum of the resistance of all the resistors when
they are connected in series.
R=R,+R,+R, +…

Parallel Connection:
• The current completes the circuit by getting divided into each branch since
the resistors are connected in parallel.
The total current in the circuit is the sum of the current through all the branch circuits
Effective resistance,

Resistors in series
• Only one path for current flow in a closed circuit. • Effective resistance increases
•The current through each resistor is same.
•The potential difference across each resistor is different. It gets divided as per the value of resistors.
• Each resistor cannot be controlled by using separate switches.

Resistors in parallel
• Effective resistance decreases.
The current through each resistor is different. It gets divided as per the
value of resistors.
• The potential difference across each resistor is same. • Each resistor can be controlled by using separate switches.

Heating effect of Electricity – Uses
Heating Coils:
• It is an electrical device that converts current to heat • Heating coil (Main part)
Heating coils are made of Nichrome
• Nichrome is an alloy of nickel, chromium and iron.

The peculiarities of Nichrome
1. High resistivity 2. High melting point (1400°C) 3. ability to remain in red hot condition for a long time without getting
4. The substance is high resistance to corrosion. 5. The operating temperature is 900°C

Safety fuse

  • Safety fuse is a device that works on the heating effect of electric current.
  • The Main Part is Fuse wire
  • Fuse wire is made of Alloy of tin and lead
  • Fuse wire has low melting point.
  • The fuse wire connected to a circuit in series.
  • Safety fuse is a mechanism to safe electrical appliances by stopping huge current due to short circuit or overloading in a circuit.
  • When an excessive current flows through it, the wire melts and the circuit is broken.
  • In each circuit the fuse wire should be used in accordance with the current flowing through it.Safety fuse is a device which protects us and the appliances from danger
  • when an excess current flows through the circuit.

•The amount of energy consumed by an electrical appliance in unit time is its power.
The unit of heat is joule (J)
The unit of power is joule/second (J/s) or watt • The unit of power is watt (W)

  • Different Types of Lamp
    • Incandescent lamp
    • Discharge lamp
    • Fluorescent lamp
    • CFL
    • Arc lamp
    • LED Bulb

Incandescent lamp

  • Working: Heat is produced when current flows through the tungsten filament and produces white light.
  • Main part is Filament,Filament is made of tungsten.
  • Tungsten can become white hot and emit white light for a long time. In order to avoid oxidation of tungsten, the bulb is evacuated. The presence of inert gases with low pressure in the incandescent bulb helps to reduce the evaporation of the filament. Nitrogen is usually used for this purpose now.
  • At normal temperature and pressure, nitrogen behaves like an inert gas.
  • Small increase in temperature does not influence the expansion of nitrogen.
  • Major part of energy supplied filament lamp is lost as heat. Hence the
  • efficiency of these devices is less.
  • Properties of tungsten:
    • 1. High resistivity.
    • 2. High melting point high ductility.
    • 3. Ability to emit white light in the white-hot condition.
    • 4. Highest tensile strength.
    • 5. Excellent corrosion resistance.
    • 6. It is malleable

Discharge lamps

  • • Discharge lamps are glass tubes fitted with two electrodes.
  • Working: When a high potential difference is applied the gas molecules get excited. Excited atoms come back to their original states for attaining stability. During this process the energy stored in them will be radiated as light
  • • Depending on the difference in the energy levels lights of different colours
  • and other radiations are emitted.

LED bulb

  • • LEDs are Light Emitting Diodes.
  • • As there is no filament, there is no loss of energy in the form of heat.
  • • Since there is no mercury in it, it is not harmful to environment.
  • • Very small in size
  • • Lower power consumption.
  • Energy Efficient.
  • • Durable Quality.
  • • Provide long life span.

Related Articles

Leave a Reply

Your email address will not be published.

Back to top button