- Electric energy from a cell is used to do work on charges, which is converted into heat in a resistor or other forms, like motion in a motor.
- The work done (energy) in moving a charge Q across a potential difference VAB is:
Work = VAB × Q - Heat produced (H) in a resistor over time t is given by Joule’s Law of Heating:
H = I2 × R × t - According to Ohm’s Law:
VAB = I × R - Electrical power (P) is the rate of energy transfer and is calculated as:
P = VAB × I
Its unit is watt (W), where 1W = 1 volt × 1 ampere.
Definitions [5]
Define fuse.
Electric fuse is a safety device which is used in household wiring and in many appliances.
Define the following:
Electrolyte
The solution through which the electricity passes is called an electrolyte.
Definition: Heating effect of electric current
When a resistor is connected in an electrical circuit, heat is produced in it due to the current. This is known as the heating effect of current.
Define Electric power.
Electric power (P) is the rate at which electrical energy is transferred or consumed in an electrical circuit.
Definition: Electric Power
In an electrical circuit, electric power is defined as the rate at which electrical energy is supplied by the source.
Formulae [2]
Write the mathematical expression for Joule’s law of heating.
The mathematical expression of Joule’s Law of heating is: H = I2 Rt
Where,
H = Produced Heat
I = Current flowing through the device
t = Time taken
r = Resistance of the appliance
Formula: Electric Power
Electric Power P = \[\frac {W}{t}\] = VI = \[\frac {V^2}{R}\] = I2R
Key Points
Key Points: Electric Circuit
Key Points: Series Combination of Resistors
- In series, resistors are connected one after another (in a single path).
- Current is the same through all resistors.
Equivalent resistance:
Req = R₁ + R₂ + R₃ + ...
For n identical resistors:
Req = nR
Voltage relation:
V = V₁ + V₂ + V₃
Voltage divider rule:
V₁ : V₂ : V₃ = R₁ : R₂ : R₃
Req > Rmax
Key Points: Parallel Combination of Resistors
- In parallel, resistors are connected across the same two points (multiple paths).
- Voltage is the same across all resistors.
Equivalent resistance:
\[\frac{1}{R_{eq}}=\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}+\cdots\]
For n identical resistors:
Req = R/n
Current relation:
I = I₁ + I₂ + I₃
Current divider rule:
I₁ : I₂ : I₃ = \[\frac{1}{R_{1}}:\frac{1}{R_{2}}:\frac{1}{R_{3}}\]
Req < Rmin
Key Points: Heating Effect of Electric Current
- Heating Effect: Current through a resistor produces heat, calculated by H = I²Rt or H = VIt (Joule’s Law).
- Heat Applications: Used in devices like irons, heaters, bulbs, and fuses (to stop excess current).
- Power Unit: 1 kWh = 3.6 × 10⁶ J, called 1 unit of electrical energy in electricity bills.
- Short Circuit & Fuse: A short circuit causes a large current; the fuse wire melts to break the circuit and prevent fire.
- MCBs: Miniature Circuit Breakers automatically cut off power during overload or fault conditions.
Key Points: Electric Power
- Electrical power represents the rate at which electrical energy is supplied by the source in an electric circuit.
- The S.I. unit of electrical power is a watt (W), and larger units such as kilowatt, megawatt, and gigawatt are used for measuring higher power.
Important Questions [33]
- Match the Column ‘A’ with Column ‘B’.
- Two Tungsten Bulbs of Power 50 W and 60 W Work on 220 V Potential Difference. If They Are Connected in Parallel, How Much Current Will Flow in the Main Conductor?
- The unit of electrical power is _______.
- In Series Combination Which Remains Constant?
- Find the Expression for the Resistors Connected in Series and Write the Two Characteristics of It.
- Complete the Following
- If the Equivalent Resistance is to Be Increased, Then the Number of Resistances Should Be Connected in
- Find the Expression for Resistors Connected in Series.
- Write Any Two Characteristics of a Series Combination of Resistors.
- To Increase the Effective Resistance in a Circuit, the Resistors Are Connected in _______________ .
- Choose the Correct Alternative and Rewrite the Following Sentence. If Three Resistors 2 Ohms, 3 Ohms and 4 Ohms Are Connected in Series,
- Choose the Correct Alternative and Rewrite the Following: You Are Given Three Equal Resistances. in How Many Combinations Can They Be Arranged?
- When Do You Say that the Resistors Are Connected in this Way? Draw a Circuit Diagram.
- The Equivalent Resistance of the Parallel Combination of Two Resistors of 60ω and 40ω is _______.
- Differentiate Between Resistances in Series and Parallel.
- Complete the Following
- Complete the Following
- The Equivalent Resistance of a Parallel Combination of Two Resistors of 30 ω and 60 ω is ______________
- With a Neat Labelled Diagram and Derive the Equation for Three Resistances Connected in Parallel.
- Identify the figure and give its use.
- State Four Most Common Electrical Appliances Based on Heating Effect of Electric Current. Why Do We Use Finely Heated Platinum Wire in Surgery?
- Give scientific reason : In the electric equipment producing heat e.g. iron, electric heater, boiler, toaster etc., an alloy such as Nichrome is used, not pure metals.
- Name Any Six Domestic Appliances Based on the Heating Effect of Electric Current.
- Rewrite the Following Statement by Selecting the Correct Option: 1 a = ____________ Ma.
- Answer the Following Question: What is the Heating Effect of the Electric Current? State Any Four Applications of It?
- Give a scientific reason. Tungsten metal is used to make a solenoid type coil in an electric bulb.
- Give a scientific reason: For electric power transmission, copper or aluminium wire is used.
- Identify the figure and give its use.
- Define Electric power.
- If a Bulb of 60w is Connected Across a Source of 220v, Find the Current Drawn by It.
- What is meant by "electric power"?
- 1 Calorie = _________ Joule.
- An Electric Iron Rated 750 W is Operated for 2 Hours/Day. How Much Energy is Consumed by the Electric Iron for 30 Days?
