The sun rays reach the earth’s surface by

1. Analyze the question The question asks how heat and light energy from the sun travel through space to reach the earth. We need the mode of energy transfer.

2. Explain the concept There are three ways heat energy is transferred:

• Conduction: transfer through direct contact, mainly in solids, by particle vibration. It needs a medium.
• Convection: transfer through the movement of fluids (liquids and gases). It also needs a medium.
• Radiation: transfer by electromagnetic waves. It needs no medium and can travel through a vacuum.

Reflection (bouncing of light off a surface) and refraction (bending of light as it passes from one medium to another) are behaviours of light. They are not ways energy is transferred over long distances.

3. Show the solution

• Between the sun and the earth there is mostly empty space (a vacuum).
• Conduction and convection need particles to carry the energy, so they cannot work across space.
• Only radiation can travel through a vacuum, as electromagnetic waves (visible light, infrared, and ultraviolet).
• So the sun's rays reach the earth by radiation.

4. Answer The correct option is C. radiation.

5. Tip Remember: "Radiation = Rays." The sun's rays come by radiation. If the question involves space or a vacuum, rule out conduction and convection straight away, because both need particles.