If your local electricity cost 8 cents/kwh, determine how much it costs to run the following: a. a 100 w lamp for 10 h. b. a 400 w tv for 8.0 h c. a 1200 w microwave oven for 15.0 min

a) 8 cents

b) 25.6 cents

c) 2.4 cents

Explanation:

Given:

Cost of electricity = 8 cents/kWh

Total cost = Wattage ×Time × Electricity cost

a) cost of running a lamp of 100 W for 10 h will be

Energy consumed = 100 W ×10 h = 1000 Wh or 1 kWh  [1 kW = 1000 W]

Total cost = Energy consumed × electricity cost

⇒Total cost = 1 kWh × 8 cents/kWh = 8 cents

b) cost of running a TV of 400 W for 8 h will be

Energy consumed = 400 W × 8 h = 3200 Wh or 3.2 kWh  

Total cost = Energy consumed × electricity cost

⇒Total cost = 3.2 kWh × 8 cents/kWh = 25.6 cents

c) cost of running a microwave of 1200 W for 15 min will be

Energy consumed = 1200 W × = 300 Wh or 0.3 kWh    [1h = 60 min]

Total cost = Energy consumed × electricity cost

⇒Total cost = 0.3 kWh × 8 cents/kWh = 2.4 cents

5 w for 1hr = 5x60x60 joules=300x60=3000x6=18,000j as total energy conversion. efficiency of bulb needed for radiant to thermal within 18000