Tag: physics

Electricity used in homes is made at a power plant by huge generators. Most power plants use coal, but some use natural gas, water or even wind.

Electricity used in homes is made at a power plant by huge generators. Most power plants use coal, but some use natural gas, water or even wind.

Answer is A.

The total energy consumed is 3 units = 3 kWh = 3000 Wh.
The total enrgy dissipated is given as Power * Time.
Therefore, time = Energy dissipated / Power.
Time taken = 3000 Wh / 60 W = 50 hours.
Hence, an electric fan marked 60 watt consumes 3 units for the duration of 50 hours.

Electricity generated at power station is AC usually $11  KV$ to $22  KV$.

The unit of electricity for domestic use is 'KWh'(KiloWatt-hour)

% Watt hour efficiency = $\frac{E _{out}} {E _{in}} \times 100$
= $\frac{\left ( 14 \right )\left ( 5 \right )\left ( 15 \right )} {\left ( 15 \right )\left ( 10 \right )\left ( 8 \right )} \times 100 = 87.5$%

One of the key concerns in the transmission of electricity is the power loss in transmission lines, dissipated as heat due to the resistance of the conductors.
The power loss ${P} _{loss} = { I }^{ 2 }R={ (\dfrac { P }{ V } ) }^{ 2 }R(\because p=VI)$
Since $P $and $R $ are fixed conditions, less power will be lost if high voltages V are used.
The transmission line then uses a transformer to step down the voltage.
For a given amount of power, a higher voltage reduces the current and thus the resistive losses occurs in the conductor. For example, raising the voltage by a factor of 10 reduces the current by a corresponding factor of 10 and therefore the$ {I}^{2}{R}$ losses by a factor of 100, provided the same sized conductors are used in both cases. 

Total length of wire = $20 \times 2 = 40km$