Class X - SSLC - Physics Quick Notes : 1 - Effects of Electric Current

• 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 current.
  
  H = I²Rt Joule
  Where I is the current in ampere, R is the resistance in ohm and t is the time in second.
• When the current in the circuit is doubled, heat generated becomes four times.
• If the current is halved, heat generated becomes  1/4 times.
• Instruments that make use of heating effects of electric current are electric heating appliances.
• In electric heating appliances heat is produced in heating coil.
• Fuse wire has low melting point.
• During overloading and short circuit the fuse wire melts and circuit breaks.
• In incandescent lamps filaments are made up of tungsten metal.
• Tungsten metal has high resistivity and high melting point. 
• LED lamp gives more light but consumes less electrical energy. 
• Effective resistance is the sum of the resistance of all the resistors 
• Heating coils are made up of Nichrome.
• Nichrome has high melting point and high resistivity.
• Safety fuse is a device that works on the heating effect of electric current.
• In order to avoid oxidation of tungsten, the bulb is evacuated, or filled some inert gas at low pressure or filled with nitrogen.
• Color of light emitted from a discharge lamp depends on the gas filled inside the lamp.
• Effective resistance is the sum of the resistance of all the resistors when they are connected in parallel when they are connected in series, ie,
  R = R₁ + R₂
• Effective resistance is the sum of the reciprocal of all the resistors when they are connected in parallel$$\frac{1}{R}= \frac{1}{R_{1}} + \frac{1}{R_{2}} or    R=    \frac{R_{1}R_{2}}{R_{1}+{R_{2}} }$$
• If resistors of the same value are connected in parallel, then  $$R = \frac{r}{n}$$Where n is the number of resistors and r is the resistance of one resistor.
• The amount of energy consumed by an electrical appliance in unit time is power.
• Units of power is watt(w)
• Electric power (P) = I²R  $$P = \frac{V^{2}}{R} ; P = VI$$