An electric kettle has an input power of 2000 W. The useful power output, heating the water, is 1800 W.
.1
Calculate the efficiency of the kettle.
[2 marks]
.2
Calculate the power wasted by the kettle.
[1 mark]
.3
Give one way energy is wasted by the kettle.
[1 mark]
6 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
A country needs a new power station. It could build a hydroelectric power station in a mountain valley or a gas-fired power station near a town.
Comparison of two power stations. Hydroelectric: fuel cost none; carbon dioxide when generating none; start-up time about 1 minute; building cost very high; needs a flooded valley. Gas-fired: fuel cost high; carbon dioxide when generating yes; start-up time about 15 minutes; building cost medium; can be built near towns.
Feature
Hydroelectric
Gas-fired
Fuel cost
None
High
Carbon dioxide when generating
None
Yes
Start-up time
About 1 minute
About 15 minutes
Building cost
Very high
Medium
Site
Needs a flooded valley
Can be built near towns
Evaluate the two options. Use information from the table and your own knowledge.
[6 marks]
6 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
Scientists' model of the atom has changed as new evidence was found.
Describe how the model of the atom developed from the plum pudding model to the model we use today, and the evidence for the changes.
[6 marks]
6 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
An electric motor in a lift raises the lift through a height of 12 m in 20 s. The mass of the lift is 800 kg.
Gravitational field strength = 9.8 N/kg.
.1
Calculate the energy transferred to the lift's gravitational potential store.
[2 marks]
.2
Calculate the useful power output of the motor.
[2 marks]
.3
A second motor raises the same lift through the same height in 30 s.
Explain why the second motor has a lower power output.
[2 marks]
7 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
A current of 0.25 A flows through a 47 Ω resistor.
.1
Calculate the power transferred in the resistor.
Give your answer to 2 significant figures.
[3 marks]
.2
The p.d. across the resistor is 11.75 V. In one minute, 15 C of charge flows through it.
Calculate the energy transferred in one minute.
[2 marks]
.3
Show that your answers to parts 1 and 2 agree, and explain why.
