Learn Unit IV: Effects of Current with Free Lessons & Tips

(i) When the bulb starts glowing, its resistance increases due to the increase in temperature. Using Ohm's law,
R=V/I=4V/0.4A =10Ω
(ii) The reason for the difference in resistance is the phenomenon of electrical resistance increasing with temperature. When current flows through the bulb, it heats up, causing an increase in resistance.

Resistance is the opposition offered by a material to the flow of electric current. Resistivity, on the other hand, is the intrinsic property of a material that quantifies how strongly it resists the flow of electric current. The relationship between resistance (R), resistivity (ρ), and dimensions (length l, and cross-sectional area A) of the conductor is given by R=ρ⋅lA
Resistance is dependent on temperature, increasing with an increase in temperature for most conductors due to increased collision frequency of charge carriers with lattice ions, which impedes their flow.

The resistance of the bulb can be calculated using Ohm's law: R=V/I=330V/110W=3Ω The energy consumed by three bulbs burning for 5 hours is E=P⋅t=110W×3×5h=1650Wh=1.65kWh The cost in rupees is calculated as Cost=Energy consumed×Rate=1.65kWh×0.70 Rupees/kWh=1.155

The resistance of the copper wire can be calculated using the formula R=ρ⋅l/A, where ρρ is the resistivity of copper, ll is the length of the wire, and AA is the cross-sectional area of the wire. Given ρ=1.72×10−8 Ω⋅mρ=1.72×10−8Ω⋅m, l=2 km=2000 ml=2km=2000m, and r=2 mm=0.002 mr=2mm=0.002m (radius),the cross-sectional area A=πr2=π×(0.002)2 m2A=πr2=π×(0.002)2m2. Substituting these values into the formula gives R=(1.72×10−8 Ω⋅m)×(2000 m)π×(0.002)2 m2R=π×(0.002)2m2(1.72×10−8Ω⋅m)×(2000m). Calculating this expression gives the resistance of the wire.

a. When the magnitude of electric current in the wire is increased, the compass needle deflects more, showing a stronger magnetic field around the wire. b. The compass needle is deflected away from the wire because the direction of the magnetic field produced by the current in the wire is opposite to the direction of the magnetic field of the compass needle.

• A fuse is placed in series with an electrical appliance in a circuit to protect the appliance and the circuit from damage due to excessive current. A fuse with a defined rating should not be replaced by one with a larger rating because a larger-rated fuse may allow too much current to pass through the circuit, risking damage to the appliance and causing a potential fire hazard.