Efficiency

Fig. 2.1 illustrates an electric motor lifting a load. The load, which has a weight of $5.0\,\text{N}$, is lifted vertically through $3.5\,\text{m}$ at constant speed. The efficiency of the electric motor is $0.65$ (65%).

May/June 2016

The combined area of three solar panels is $7.2\,\text{m}^2$. In total, they deliver $1.0\,\text{kW}$ of power. For each panel, an area of $1.0\,\text{m}^2$ receives $0.80\,\text{kJ}$ of energy from the Sun in $1.0\,\text{s}$. What is the efficiency of the solar panels?

May/June 2019

Fig. 9.1 illustrates how energy is converted in a mobile phone.

May/June 2021

In $1.0\,\text{s}$, the energy received per unit area by a set of solar panels is $120\,\text{J m}^{-2}$. During $1.0\,\text{s}$, the set of solar panels changes $720\,\text{J}$ of light energy into $120\,\text{J}$ of useful electrical energy. What is the total surface area of the panels, and what is the efficiency of the system?

May/June 2022

A kettle receives $600\,\text{kJ}$ of electrical energy. From this energy, $45\,\text{kJ}$ is passed to the surroundings and $15\,\text{kJ}$ is used in heating the kettle casing. The energy left over is transferred to the water. What is the efficiency of the kettle?

May/June 2022

A lamp receives an input power of $6.0\,\text{W}$. Over $3.0\,\text{s}$, it loses $2.7\,\text{J}$ of energy as waste. Calculate the efficiency of the lamp.

May/June 2024

A $15\,\text{W}$ lamp is switched on for $30$ minutes. It wastes $7000\,\text{J}$ of energy. Calculate the lamp’s efficiency.

May/June 2024

A lamp receives an input power of $6.0\,\text{W}$. In $3.0\,\text{s}$, the lamp loses $2.7\,\text{J}$ of energy. What is the efficiency of the lamp?

Oct/Nov 2015

A major power station burns oil in order to heat water inside a boiler.

Oct/Nov 2016

An electric motor connected to the mains is used to raise bricks up to the top of a building. A fuse is fitted in the plug. How could the efficiency of the motor be improved?

Oct/Nov 2018

Information for three kinds of electricity generator is shown. Which generator is the least efficient, and which is the most efficient?

Oct/Nov 2020

Which equation is used to calculate the efficiency of an energy transfer?

Oct/Nov 2021

X and Y are both $40\,\text{W}$, $240\,\text{V}$ lamps. Lamp X is more efficient than lamp Y. Which statement gives the correct comparison between X and Y?

Oct/Nov 2022

A motor receives an input power of $12\,\text{W}$. Over $1.0\,\text{min}$, it loses $590\,\text{J}$ of energy. Calculate the efficiency of the motor.

Oct/Nov 2022

Electric motors have an efficiency of about $90\%$ when they are used in an electric train. What forms of wasted energy are generated?

Oct/Nov 2022

An electric motor is employed to raise a load at constant speed. The gravitational potential energy (GPE) stored in the load rises. The moving load also possesses kinetic energy (KE). Which expression is used to calculate the efficiency of the motor while the load is lifted at a constant rate?

Oct/Nov 2023

A wind-up radio is used in places where mains electricity is unavailable. A person turns a handle to wind a spring inside the radio. As the spring unwinds, it causes a small coil to rotate in a magnetic field. Which energy transfer is not useful for this radio?

Oct/Nov 2024

A filament lamp transfers energy at a rate of $60\,\text{W}$. It dissipates energy at a rate of $46\,\text{W}$. Which ratio should be used to determine the efficiency of the lamp?

Oct/Nov 2024

Which equation is used to work out the efficiency of an energy transfer?

Oct/Nov 2024

What does the term efficiency mean?

Oct/Nov 2025