Power of devices All domestically available appliances and devices have a power rating on them.This allows the user to calculate the energy requirement per second of use of the appliance. For example, one can buy 100 W light bulbs or ‘energy saving’ ones that are as low as 7 W.Typically heating appliances have high power ratings, a 3 kW kettle for example, while often larger appliances such as a washing machine may be 500 W, while a DVD player is of the order of 50 W. It is important to take notice of the power rating of an appliance so as to reduce energy usage where possible.
‘SECTION B’ SHORT QUESTIONS
Typical of Question 5 in Leaving Cert. Exam
Q1 Answer all of the following parts (a), (b), (c), etc. (a) Define the concept of work.
(b) Which of the following is not a unit of energy? electronvolt kilowatt hour kelvin joule
(c) Other than potential and kinetic, list two types of energy.
(d) Which of the following is a renewable source of energy? coal biomass nuclear oil (7)
(e) Why is nuclear energy sometimes advocated by individuals concerned for the environment yet discouraged by other equally concerned people? (7)
(f) Calculate the potential energy of the FA Premiership trophy which Ryan Giggs held overhead after winning his eleventh league title in 2009.The trophy has a mass of 15 kg and he held it 1.9 m above the ground.Acceleration due to gravity is 9.8 m s2. (7)
(g) Why is a filament light bulb not an efficient source of energy? (7)
(h) Define power. (7)
(i) A ghd hair straightener has a power rating of 1 400 W. Calculate the energy used by the straightener when turned on for 20 minutes. (7)
(j) A toaster has a power rating of 1 050 W when it is connected to the mains supply. Calculate the power output if it has an efficiency of 96 per cent. (7)
Ryan Giggs holds up the FA Premiership trophy in 2009
