TOEFL Readings 58

ImageA summary of the physical and chemical nature of life must begin. not on the Earth. but in the Sun. in fact. at the Sun's very center. It is here that is to be found the source of the energy that the Sun constantly pours out into space as light and heat.

This energy is liberated at the center of the Sun as billions upon billions of nuclei of hydrogen atoms collide with each other and fuse together to form nuclei of helium. and, in doing so. release some of the energy that is stored in the nuclei of atoms. The output of light and heat of the Sun requires that some 600 million tons of hydrogen be converted into helium in the Sun every second. This the Sun has been doing for several thousands of millions of years.

The nuclear energy is released at the Sun's center as high-energy gamma radiation, a form of electromagnetic radiation like light and radio waves, only of very much shorter wavelength. This gamma radiation is absorbed by atoms inside the Sun, to be re-emitted at slightly longer wavelengths. This radiation, in its turn, is absorbed and re-emitted. As the energy filters through the layers of the solar interior, it passes through the x-ray part of the spectrum, eventually becoming light. At this sage, it has reached what we cal: the solar surface, and can escape into space. without being absorbed further by solar atoms. A very small fraction of the Sun' s light and heat is emitted in such directions that, after passing unhindered through inter-planetarv, space,  It hits the Earth.

1. What does the passage mainly discuss?

(A) the production of solar light and heat

(B) the physical and chemical nature of life

(C) The conversion of hydrogen to helium

(D) Radiation in the x-ray part of the spectrum

2. According to the passage, energy is released in the Sun when

(A) helium atoms bind with each other

(B) gamma radiation escapes from the spectrum

(C) radiation is absorbed by helium

(D) nuclei of hydrogen atoms collide

3. The passage indicates that, in comparison to radio waves, gamma waves

(A) produce louder sound

(B) are less magnetic

(C)  do not form in the Sun's center

(D) are not as long

4. According to the passage, through which of the following does the energy released in the Sun pass before it becomes light?

(A) The x-ray part of the spectrum

(B) Electromagnetic space

(C) The solar surface

(D) interplanetary space

5. It can be inferred from the passage that the Sun's light travels

(A) through solid objects in space

(B) in many different directions

(C) more slowly than scientists previously believed

(D) further in summer than in winter