Grade 8 Science Practice Test: Light Waves and the Electromagnetic Spectrum
- Light Waves and the Electromagnetic Spectrum
- 10 questions
- 13 minutes
Ten questions on light and the other waves of the electromagnetic spectrum. Tip: as you move from radio waves to gamma rays, wavelength gets shorter while frequency and energy go up.
Tap an option to mark your answer. You can change your mind, or tap the same option again to leave the question blank. The correct answers and explanations appear when you finish the test.Tap an option to answer; tap it again to leave the question blank.
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Question 1
Which type of electromagnetic wave has the longest wavelength?
Correct answer: D
Radio waves are at the long-wavelength end of the spectrum and can be longer than a building. Gamma rays are at the opposite, short end.
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Question 2
Which type of electromagnetic wave carries the most energy?
Correct answer: A
Energy rises with frequency, and gamma rays have the highest frequency in the spectrum. Radio waves carry the least energy.
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Question 3
How does the speed of different electromagnetic waves compare in empty space?
Correct answer: C
All electromagnetic waves travel at the speed of light in a vacuum, about 300,000 km per second. They differ in wavelength and frequency, not speed.
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Question 4
How are light waves different from sound waves?
Correct answer: B
Sound is a vibration of matter and needs a medium, but light can cross the vacuum of space. That is why we see the Sun but cannot hear it.
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Question 5
A straw in a glass of water looks bent at the water's surface. What causes this?
Correct answer: C
Light changes speed and bends when it passes from water into air; this bending is refraction. Reflection is light bouncing off a surface.
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Question 6
Why does a red apple look red in white light?
Correct answer: D
White light contains all colors. The apple's surface absorbs most of them and reflects red, which reaches your eyes. If it absorbed red, it would not look red.
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Question 7
Two light waves travel at the same speed. Wave X has a higher frequency than wave Y. How do their wavelengths compare?
Correct answer: A
At a fixed speed, wavelength and frequency are inversely related: more waves per second means each wave is shorter. Speed = frequency x wavelength.
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Question 8
A ray of light strikes a flat mirror at an angle of 30° to the normal (the line perpendicular to the mirror). At what angle to the normal does it reflect?
Correct answer: B
The law of reflection says the angle of reflection equals the angle of incidence, both measured from the normal. 60° would be the angle to the mirror's surface, not to the normal.
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Question 9
Which type of radiation from the Sun causes sunburn?
Correct answer: C
Ultraviolet light has enough energy to damage skin cells, which is why sunscreen blocks UV. Infrared is felt mainly as warmth.
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Question 10
Why are digital signals usually more reliable than analog signals for sending information?
Correct answer: A
A digital receiver only has to tell a 1 from a 0, so small disturbances are ignored and copies stay exact. In an analog signal, noise changes the wave itself.
Questions you leave blank are not counted as wrong.
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