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Question 1

The Sun puts out an incomprehensible amount of energy—so much that its ultraviolet radiation can cause sunburns from ……… …….. ……… away.

Answer 1

93 million miles

Question 2

As you learned earlier, evidence shows that the Sun formed about ………. ………… years ago and has been shining ever since.

Answer 2

4.5 billion

Question 3

The Sun’s energy output is about ……… ……..

This is unimaginably bright: brighter than a trillion cities together each with a trillion 100-watt light bulbs.

Answer 3

4 × 10²⁶ watts

Question 4

A watt (W) is a unit of power, which is energy used or given off per unit time. It is measured in …….. ……. ……….

Answer 4

joules per second (J/s)

Watts tell you the rate at which energy is being used; for example, a 100-watt bulb uses 100 joules (J) of energy every second.

Question 5

In the nineteenth century, scientists thought that the source of the Sun’s heat might be the mechanical motion of ………… falling into it.

Answer 5

meteorites

Question 6

British physicist …….. ……… and German scientist ……… ………. ………. proposed that the Sun might produce energy by the conversion of gravitational energy into heat. In other words, proposed that the Sun could be shrinking in size, staying hot and bright as a result.

Answer 6

Lord Kelvin / Hermann von Helmholtz

Question 7

As we have seen, energy cannot be created or destroyed, but only converted from one form to another. One of the remarkable conclusions derived by Albert Einstein when he developed his theory of relativity is that matter can be considered a form of energy too and can be converted into energy. Furthermore, energy can also be converted into matter. This seemed to contradict what humans had learned over thousands of years by studying nature. Matter

Answer 7

R 2

Question 8

The remarkable equivalence between matter and energy is given in one of the most famous equations:

Answer 8

E=mc^2

• E stands for energy,
• m stands for mass, and
• c, the constant that relates the two, is the speed of light (3 × 10⁸ meters per second).

Question 9

Scientists soon realized that the conversion of ………… into energy is the source of the Sun’s heat and light.

Answer 9

mass

Question 10

We can calculate that the amount of energy radiated by the Sun could be produced by the complete conversion of about …….. ……… ……….. of matter into energy inside the Sun each …………

Answer 10

4 million tons / second

Question 11

Protons, neutrons, and electrons are not all the particles that exist. First, for each kind of particle, there is a corresponding but opposite ………….. If the particle carries a charge, its ……………. has the opposite charge.

Answer 11

antiparticle

Question 12

The antielectron is the ………….., which has the same mass as the electron but is positively charged. Similarly, the antiproton has a negative charge.

Answer 12

positron

Question 13

The remarkable thing about such antimatter is that when a particle comes into contact with its antiparticle, the original particles are …………., and substantial amounts of energy in the form of ………. are produced.

Answer 13

annihilated / photons

Question 14

individual antiparticles are found in ………. ………… (particles that arrive at the top of Earth’s atmosphere from space) and can be created in ………. ………….

Answer 14

cosmic rays / particle accelerators

Question 15

antimatter is created in the core of the ……… and other ……….

Answer 15

Sun / stars

Question 16

physicist Wolfgang Pauli suggested the existence of ……………..

Answer 16

neutrino

Energy seemed to disappear when certain types of nuclear reactions took place, violating the law of conservation of energy. Pauli was reluctant to accept the idea that one of the basic laws of physics was wrong, and he suggested a “desperate remedy.” Perhaps a so-far-undetected particle, which was given the name neutrino

Question 17

The elusive neutrino was not detected until 1956. The reason it was so hard to find is that neutrinos interact very ………… with other matter and therefore are very difficult to detect.

Answer 17

weakly

Question 18

Earth is more transparent to a neutrino than the thinnest and cleanest pane of glass is to a photon of light. In fact, most neutrinos can pass completely through a star or planet without being absorbed.

Answer 18

R 2

Question 19

Answer 19

Question 20

Answer 20

Question 21

Answer 21

Question 22

Answer 22

Question 23

The nucleus of an atom is not just a loose collection of elementary particles. Inside the nucleus, particles are held together by a very powerful force called the ……….. ………. ………….

Answer 23

strong nuclear force

Question 24

This is short-range force (strong nuclear force), only capable of acting over distances about the size of the ………….. …………

Answer 24

atomic nucleus

Question 25

The strong nuclear force is an attractive force, stronger than the electrical force, and it keeps the particles of the nucleus tightly bound together despite these having same charge and feel repulsed by each other

Answer 25

R 2

Question 26

if particles come together under the strong nuclear force and unite to form an atomic nucleus, some of the nuclear energy is released. The energy given up in such a process is called the ……….. ……… of the nucleus.

Answer 26

binding energy