Question

plese Solve Que 4-10

Answer 1

4. H = I² R t = V²/R * t = I² * ρ L / A * t
    Heat dissipated depends on time elapsed, voltage across resistor or current passing through it, and the resistance.  Resistance depends on the material (resistivity , length and area of cross section).

5.   R = ρ L / A
      Resistivity ρ is the resistance R of a substance of 1 meter length L and 1 m^2 cross sectional area A.   SI units:  Ohm-m.

6. ρ depends on substance, length, cross section and the temperature.
     i) choose material of least resistivity
       ii) choose material of highest resistivity
      iii)  resistivity of D is 60 times.  So resistance of D = 2 * 60 = 120 Ω

7.  1 kW is a unit of power.  1 kWh  is a unit of energy.
      I = P/V
      R = V^2 / P
      Energy = P * time duration

8.  Ammeter.   Unit is Ampere.
     
9.   H = I^2 R t

10.  no they will not glow with the same power.
       Bulbs connected in parallel will glow brighter.  Because current in them is more.      P = I^2 R = V^2/R
         Voltage is divided by 3 when connected in series. It remains same when connected in parallel.  Brightness depends on the power.