71. Which electromagnetic waves with long wavelengths are used to send signals around the Earth? When their wavelengths get shorter, they are known as microwaves, infrared waves, and light.
(a) Gamma rays
(b) X-rays
(c) Ultra-violet waves
(d) Radio and television waves
72. Radioactive substances give off a stream of electrons known as beta-rays. What is caused by a moving electron?
(a) Current electricity
(b) Force
(c) Energy
(d) Magnetism
73. All matter has mass and volume, but there are some things that do not have mass or volume. These include electricity, sound, light, and heat. What are these called?
(a) Force
(b) Ultrasound
(c) Ultra particles
(d) Energy
74. Electromagnetic waves with long wavelengths are used to send signals around the Earth. When the wavelengths get shorter, they are known as microwaves and infrared waves and light. What are the waves with a shorter wavelength than light called?
(a) Gamma rays
(b) X-rays
(c) Ultra-violet waves
(d) All of these
75. Pick out the red-brown metal that was the first metal used to make tools and weapons and is a very good conductor of heat and electricity.
(a) Iron
(b) Lead
(c) Copper
(d) Silver
76. What is called the machine that transforms energy into useful mechanical work?
(a) Engine
(b) Machine
(c) Tools
(d) None of these