Calculate the efficiency of a hair dryer which takes in 4500J of energy per second and transfers 150J as useful heat energy.

η = 0.0333 = 3.33 %

Explanation:

The efficiency of any device is defined as the ratio of the useful output obtained from that device to the input required by the device. Therefore, the general formula to find the efficiency of any device is given as follows:

where,

η = efficiency of hair dryer = ?

O = Useful Output Given by the Hair Dryer = 150 J

I = Input Energy Required by the Hair Dryer = 4500 J

Therefore,

η = 0.0333 = 3.33 %

answer: 802.3 kilo joules of energy represents 191.75 kilo calorie of energy.

explanation:

energy released during combustion of one mole methane = 802.3 kilo joules

if 1 kilo joule = 0.239006   kilo calorie

then ,802.3 kilo joule will be = 802.30.239006 kilo calorie

802.3 kilo joule = 191.75 kilo calorie

hence, the energy in kilo calorie is 191.75 kilo calorie.