Basic electricity & incandescent bulb numericals--plzzz my test is near!

Discussion in 'Homework Help' started by flabber, Feb 1, 2009.

  1. flabber

    Thread Starter New Member

    Jan 23, 2009
    hi there, i hav few test is very near plz help me soon :(:(

    1. A 12V, 24W tungsten filament bulb is supplied with current from n cells connected in series. Each cell has an emf of 1.5V and internal resistance of 0.25. What is the value of n in order that the bulb runs at its rated power?

    2. Three bulbs are rating 40W, 60W, 100W designed to work on 220V mains. Which bulb will burn most brightly if they are connected in SERIES across 220V mains? Repeat the same question when they are connected in PARALLEL across 220V.

    3. An electric iron is marked 20 Volts, 500W. what will be The units consumed by it in using it for 24 hours?

    4. What is the heat generated by a 40 W bulb in one hour?

    please someone help me wid these numericals, i wud be highly grateful!
  2. beenthere

    Retired Moderator

    Apr 20, 2004
  3. Tesla00010010


    Jun 20, 2008
    1)bulb resistance: V^2/R equals W,then R is 6 ohm
    calculate amps.To find n: 1.5n equals (0.25n+6)*x
    x is the number of amps
    2)Calculate resistance using P=VI,and ohms' law.If current in the circuit is the same for all the bulbs then which bulb will burn more brightly?Proceed similar for the parallel circuit,remember current is different in each branch of a parallel circuit
    3)I guess you need to get the power consumed,power is the rate of energy consumption: Watt=Joule/Second,but in electricity you normally express in units called kilowatt-hour
    4)heat is measured in calories and1 joule=0.24 calories,finish it yourself