physics imp notes

• Calculate the combined resistance, current flowing in the main circuit, and current flowing in the 3 Ω resistor for resistors of 3 Ω and 6 Ω connected in parallel with a potential difference of 6V
• Calculate the current through the 6 Ω resistor and the potential difference across the 12 Ω resistor for the circuit shown
• For resistances of 4 Ω and 12 Ω connected in parallel across a 9V battery, determine the equivalent circuit resistance, supply current, and current in each resistor
• For three identical lamps connected in series across a 150V supply, state the voltage across each lamp and the effect of lamp C failing
• For three resistors connected in series with measured potential differences of 5V, 7V, and 10V and a supply current of 2A, determine the supply voltage, total circuit resistance, and values of the resistors
• If three identical lamps are connected in parallel with a combined resistance of 150 Ω, find the resistance of one lamp
• Weekly cost of electricity to the business can be calculated by finding the total energy used by the fires and lights and multiplying by the cost per unit
• The relationship between voltage and current is called the IV characteristic
• The resistance of a resistor can be calculated from the slope of the IV characteristic graph
• When a 12 V battery is connected to a resistor with a current of 2.5 mA, the resistance is 4.8 kΩ
• In a series circuit with resistors of 0.2 Ω, 0.3 Ω, 0.4 Ω, 0.5 Ω, and 12 Ω connected to a 9 V battery, the current through the 12 Ω resistor is 0.671 A
• Four 176 Ω resistors are needed in parallel to carry 5 A on a 220 V line
• To achieve a resistance of 9 Ω, two 6 Ω resistors are connected in parallel
• To achieve a resistance of 4 Ω, two 6 Ω resistors are connected in series
• 110 electric bulbs rated at 10 W each can be connected in parallel on a 220 V line with a maximum current of 5 A
• Tungsten is used for electric lamp filaments due to its high melting point and resistivity
• Electric heating devices use alloy conductors for higher resistivity and heat production
• Series circuits are not used in domestic circuits to prevent voltage division and overheating of devices
• The resistance of a wire is inversely proportional to its area of cross-section
• Copper and aluminium wires are preferred for electricity transmission due to their low resistivity
• When the temperature of a metal is raised, its resistance increases
• Substance with the largest electrical resistance: rubber

  Substance with the smallest electrical resistance: silver
• Best conductor of electricity: silver
• Excellent insulator: rubber
• Wood is not a good conductor of electricity
• Two resistances are said to be in series when the current flows through one resistance before flowing through the other
• Two resistances are said to be in parallel when the current splits and flows through each resistance simultaneously
• Two different resistance combinations are possible with two equal resistors, taking both of them together
• Unit of conductance: siemens (S)
• Electric power is the rate at which electrical energy is transferred by an electric circuit
• SI unit of electrical power: watt (W)
• Product of potential difference and current is electrical power
• Power (P) can be expressed in terms of current (I) and resistance (R) as P = I^2 * R or P = V * I
• Various formulae for electric power:

  • P = I^2 * R
  • P = V * I
  • P = V^2 / R
• 220V, 100W on an electrical appliance means it operates at 220 volts and consumes 100 watts of power. Power rating refers to the amount of electrical power an appliance consumes
• Electrical appliance with the highest power rating: Electric heater

  Electrical appliance with the least power rating: Electric fan
• Electrical appliance that usually draws the highest current when operated at 220V: Electric heater

  Electrical appliance that usually draws the least current when operated at 220V: Tube light
• Electrical energy being consumed by an electrical appliance refers to the amount of electrical power used over a period of time
• SI unit of electrical energy: joule (J)
• Commercial unit of energy: kilowatt-hour (kWh)