Efficiency
In a car engine, what is the most common waste energy?
Heat
Which method of heat transfer occurs through direct contact between particles?
Conduction
Light is a form of:
A) matter
B) thermal energy
C) energy that travels as waves
D) sound energy
C. Energy that travels as waves
What happens to light as it enters the eye?
It is focussed by the cornea and lens.
What type of wave is a sound wave?
Longitudinal
A light bulb receives 100J of electrical energy and produces 20J of light energy. What is its efficiency?
(Remember: % Efficiency = (useful output / total input) x 100%)
20%
Convection occurs mainly in what state(s) of matter?
Liquids and gases
What is the speed of light in a vacuum?
300,000 km/s
How does a convex lens refract light?
It converges light rays (brings them together).
It has a short wavelength
The proportion of input energy transferred into useful output energy
Energy efficiency
Radiation transfers heat through what?
Electromagnetic waves
What is the law of reflection?
The angle of incidence is equal to the angle of reflection.
There is a thin layer on the back of the eye. What is this structure, and why is it important?
It is the retina, and it contains rods and cones that allow us to see light and colour.
Name 3 types of electromagnetic radiation.
Any 3 of the following:
Radio, Microwave, Infrared, Visible Light, Ultraviolet Light Xray, Gamma Ray
Between an LED bulb and an old incandescent bulb, which is more energy efficient and why?
The LED light, because it transfers more energy into light energy. The incandescent bulb transfers more into heat as waste energy.
Which surface absorbs the most thermal radiation?
A) Shiny silver
B) White glossy
C) Black matte
D) Mirror
C. Black matte surface
What happens to light when it strikes a black surface?
It is absorbed.
A convex mirror is what type of mirror?
A) Converging
B) Diverging
B. Diverging.
If a wave has a wavelength of 400nm and a frequency of 60 Hz, what is its wave velocity?
v = 24,000 nm/s
Why can no machine be 100% energy efficient?
Some energy is always transferred to the surroundings as heat or sound.
Why do double-walled water bottles reduce heat transfer?
They trap a layer of air that acts as an insulator.
When light moves from a medium with a lower refractive index to one with a higher refractive index, what happens to the light?
It bends towards the normal.
What two substances leak from the eye when an incision is made?
The vitreous and aqueous humours.
They absorb all colours of the visible light spectrum except green.