Current Electricity Notes by Sir Waqar Hussain

Important Easy Notes of Physics of Chapter No. 13: Current Electricity written by Professor Mr. Waqar Hussain Suib. These notes are very helpful in the preparation of Physics for students of the 12th class and these are according to the paper patterns of all Sindh Book Boards.

Summary and Contents:
Topics which are discussed in the notes are given below:
  • Definition of Electric Current with Mathematically
  • Types of Current: (i) Electronic Current (ii) Conventional Current
  • Definition of Electronic Current
  • Definition of Conventional Current
  • State and Explain Ohm’s Law with its Significance and Mathematically.
  • Limitations of Ohm’s Law
  • Graphical representation
  • Definition of Resistance and Explain
  • Factor affecting Resistance Definition of the Resistivity
  • Dependence of Resistance on temperature with Mathematically
  • Combination of Resistance:  (i) Series Combination of Resistor with Expression for Equivalent Resistance (ii) Parallel Combination of Resistors with Expression for Equivalent Resistance
  • Power Deception in Resistors
  • Definition of INTERNAL RESISTANCE
  • Definition of Electromotive Force with Mathematically
  • Definition of TERMINAL VOLTAGE
  • Differentiate between ELECTROMOTIVE FORCE and  POTENTIAL DIFFERENCE
  •  A platinum wire of diameter 0.2mm is wound to make a resistor of 4 Ω. How long a wire is needed for this purpose?
  • The resistance of a copper wire is 1.27Ω at 20°C. Find its resistance at 0°C and at 100°C. The temperature coefficient of resistivity of copper is α = 0.0039°C–1
  • You are given three resistors each of 2 ohms. How would you arrange these resistors to obtain the equivalent resistances of (i) 1.33 ohms (ii) 3 ohms (iii) 6 ohms? Also prove the result mathematically.
  • Find the equivalent resistance and the current through R3& R4. Given R1 = 20Ω, R2 = 30Ω, R3 = 20Ω, R4 = 40Ω, R5 = 10Ω
  • A battery of 24V is connected to a 10Ω load and current of 2.2 amp is drawn; find the internal resistance of the battery and its terminal voltage.
  • The resistance of a tungsten wire used in a filament of a 60-watt bulb is 240Ω when the bulb is hot at a temperature of 2020°C, what would you estimate its resistance at 20°C? (The temperature coefficient of tungsten α 0.0046/°C)
  • Find the equivalent resistance in the given circuit, current I and potential difference between ‘a’ and ‘b’: R1 = 5Ω, R2 = 2Ω, R3 = 3Ω, R4 = 6Ω, V = 6 volts
  • A 50-ohm resistor is to be wound with platinum wire, 0.1 mm in diameter. How much wire is needed (ρ = 11 x 10–8 Ωm)?
  • Two resistances of 10Ω and 50Ω are connected in series with a 6-volt battery. Calculate: i) The charges drawn from the battery per minute ii) The power dissipated in 10Ω resistance
  • A 50-ohm resistor is required from a copper wire, 0.2 mm in diameter. What is the length of the wire needed? (ρ=1.6x10–8 Ω-m)
  • A rectangular block of iron has the dimensions 1.2cmx1.2cmx15cm. (i) What is the resistance of the opposite square ends? (ii) What is the resistance between two of the rectangular faces? (The resistivity for iron at room temperature is 9.6x10^8Ωm) 
  •  In the given diagram R1 = R2 = 4 Ω and R3 = 6Ω. Calculate the current in the 6Ω resistor.
  • A water heater that will deliver 1 kg of water per minute is required. The water is supplied at 20°C and an output temperature of 80°C is desired. What should be the resistance of the heating element in water if the line voltage is 220V? (Sp. Heat of water = 4200 J/kg K).
  • A rectangular bar of iron is 2 cm х 2 cm in cross –section and 20 cm long. What is the resistance of the bar at 500˚C if ρ = 11х10–8Ω-m and α = 0.0052K–1?
  • You are given three resistors each of 2Ω. How would you arrange these to obtain equivalent resistance of: (a) 1.33Ω (b) 3Ω (c.) 6Ω. Verify the results mathematically?
  • Two resistors of 5Ωand 2Ω are connected in parallel with a 9V battery. Calculate the current and power dissipated in each resistance.
  • A rectangular bar of iron is 2 cm X 2cm in cross section an 20 cm long. What will be its resistance at 500oC? If α = 0.0052 K-1 and ρ = 11 x 10-8Ωm
  • A 50-ohm resistor is to be wound with platinum wire, 0.1 mm in diameter. How much wire is needed (ρ = 11 x 10–8 Ωm)? 

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