SCI10 Doppler effect and Red and Blue Shift

While listening to an ambulance siren passing by, you notice a change in the sound frequency. What is this phenomenon called?

• A change in colour

• A change in size

• A change in shape

• A change in weight

Answer explanation

The Doppler effect refers to the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. In the context of light, this is perceived as a change in colour. Therefore, the correct answer to the question 'What is the Doppler effect?' is 'A change in colour'.

When a car is driving away from you, the sound of its engine

• Sounds louder

• Sounds fainter

• Sounds the same

• Changes colour

Answer explanation

The phenomenon described in the question is known as the Doppler Effect. When an object is moving away from you, the frequency of the sound waves it produces decreases, which makes the sound seem fainter to your ears. This is why 'Sounds fainter' is the correct answer.

You are standing on the sidewalk and a police car with its siren on is rushing towards you. What kind of sound do you perceive?

• A higher-pitched sound

• A lower-pitched sound

• No sound

• A bird chirping

Answer explanation

When a car with a siren is approaching you, you hear a higher-pitched sound due to the Doppler effect. This phenomenon causes the frequency of the sound waves to increase as the source of the sound moves closer to the observer, resulting in a higher-pitched sound.

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You are observing a distant galaxy through a telescope. You notice that the light from the galaxy is moving towards the red end of the spectrum. What color is this phenomenon commonly associated with?

• Green

• Red

• Blue

• Yellow

Answer explanation

The term 'redshift' is associated with the color red. Redshift occurs when light or other electromagnetic radiation from an object is increased in wavelength, or shifted to the red end of the spectrum. This phenomenon is observed in astronomy and is used to measure the distance and velocity of celestial objects moving away from Earth.

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Imagine you are an astronomer observing a star through your telescope. If the star is moving away from you, how would its light appear to you?

• Red

• Green

• Blue

• Yellow

Answer explanation

The phenomenon described in the question is known as 'Redshift'. When a star is moving away from us, the light it emits shifts towards the red end of the spectrum. This is due to the Doppler effect, which causes the wavelength of the light to increase, making it appear red. Therefore, the correct answer is 'Red'.

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Imagine you are standing on the sidewalk and a police car drives past you with its siren on. Why does the sound of the siren change as it passes by?

• The siren is malfunctioning

• Doppler effect

• The siren is increasing in volume

• It's a magical phenomenon

Answer explanation

The correct answer is 'Doppler effect'. This phenomenon occurs when a source of sound, such as a police car siren, moves relative to an observer. As the police car approaches, the sound waves are compressed, making the siren sound higher-pitched. When the car passes and moves away, the sound waves are stretched, making the siren sound lower-pitched. This change in pitch is what makes the siren sound different as it drives past you.

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You are standing on the sidewalk and a blue car drives past you. What color does the car appear to be as it drives away?

• Red

• Blue

• Green

• Yellow

Answer explanation

When the blue car is coming towards you, it appears blue due to the reflection of blue light. However, as it passes you, the color remains the same, which is blue. The car does not change its color when it passes you, so the correct answer is 'Blue'.

Imagine you are sitting in a park and an ambulance passes by. What happens to the sound of the ambulance siren as it moves further away from you?

• It gets louder

• It gets quieter

• It changes colour

• It sounds like a bird

Answer explanation

As an ambulance moves away from you, the sound it produces gets quieter. This is due to the Doppler effect, which causes a change in frequency and wavelength of a wave in relation to an observer who is moving relative to the wave source. As the ambulance moves away, the sound waves are stretched out, resulting in a lower frequency and quieter sound.

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While observing a distant star, an astronomer notices a shift in the light spectrum. What color of light is associated with this "blueshift" phenomenon?

• Red light

• Blue light

• Green light

• Yellow light

Answer explanation

Blueshift is a phenomenon in which light waves are shifted towards the blue end of the spectrum. This occurs when an object emitting light is moving towards the observer, causing the wavelengths to compress and appear bluer. Therefore, the type of light associated with blueshift is blue light, which is the correct choice among the given options.

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While observing the night sky, you notice that some galaxies appear red. What could be the reason for this?

• They're painted red

• They're moving away

• They're really hot

• They like red

Answer explanation

Some galaxies look red to astronomers because they're moving away from us. This phenomenon is known as redshift, which occurs due to the Doppler effect. As galaxies move away, the light they emit gets stretched, causing the wavelengths to shift towards the red end of the spectrum. This is not because they are painted red, really hot, or have a preference for the color red.

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