experiment showing light travels in a straight line

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How to Prove That Light Travels in a Straight Path

Last Updated: April 24, 2024 Fact Checked

This article was co-authored by Chris Hasegawa, PhD . Dr. Chris Hasegawa was a Science Professor and the Dean at California State University Monterey Bay. Dr. Hasegawa specializes in teaching complex scientific concepts to students. He holds a BS in Biochemistry, a Master’s in Education, and his teaching credential from The University of California, Davis. He earned his PhD in Curriculum and Instruction from The University of Oregon. Before becoming a professor, Dr. Hasegawa conducted biochemical research in Neuropharmacology at the National Institute of Health. He also taught physical and life sciences and served as a teacher and administrator at public schools in California, Oregon, and Arizona. This article has been fact-checked, ensuring the accuracy of any cited facts and confirming the authority of its sources. This article has been viewed 215,409 times.

Light is an essential part of your day. It allows you to see objects, shapes, and colors. In fact, the pupils in your eyes filter in light to help you see everything around you. As part of a school assignment, you may be asked to prove that light travels in a straight line. You can do this using basic household items in three easy experiments.

Making a Light Pinhole

• Three index cards.
• A piece of modeling clay or sticky tack. You can also use double sided tape.

• A hole puncher.

• Take the hole puncher and punch a hole at the center of the card where the two lines intersect. Do this for the other two cards.

• Form a stand for the cards using the clay so the cards are straight and upright. Use the ruler to ensure the cards are two to five inches from each other.
• You can also use double sided tape to attach the cards to a surface in a vertical position. Do not cover or obstruct the hole in the center of the cards with modeling clay or tape.

• Note that the light can be seen through all the holes. You should be able to see the light go through all the holes and land on a wall or surface beyond the last index card.

Using a Mirror and a Flashlight

• Two to three sheets of black paper.
• Small objects like buttons, bottle caps, or dimes.

• The other person will use the small mirror to reflect the flashlight so it hits the objects. Move close to the light, at an angle, to catch the light so it hits the objects.
• You may need to position more than one mirror to create a light path that shines on the objects. Play around with reflecting the light on the mirrors until the light hits the objects. You can also move the objects around the room to create a more complicated light path, using the flashlight as the light source.
• This experiment shows that light travels in a straight line in the air. But it also bounces off of a reflective surface, like a mirror. The angle of the light as it bounces off the mirror will be the same as the angle of the light as it hits the mirror. The mirror reflects the light and changes its path from a straight line to an angled straight line.

Using Water and Oil

• A large glass jar.
• Access to water.
• One cup of oil.

• Make sure the jar is large enough to fit the ruler.

• Note that the numbers appear stretched or magnified as the light rays bend in the oil and the water. Move the ruler from side to side to note the different appearances of the ruler numbers in the oil and in the water.
• This will show that light travels at different speeds in different mediums, such as air, oil, and water. It will travel in a straight line in the air, but it will bend when it changes speed due to contact with a certain medium, like oil or water.

Expert Q&A

Things You'll Need

• A piece of modeling clay or sticky tack. You can also use tape.
• A flashlight or a laser pointer.
• A flashlight.
• A small mirror.

You Might Also Like

• ↑ http://www.ducksters.com/science/experiment_light_travel.php
• ↑ Chris Hasegawa, PhD. Retired Science Professor & Dean. Expert Interview. 29 July 2021.
• ↑ https://www.science-sparks.com/science-fair-projects-light-maze/
• ↑ https://www.scientificamerican.com/article/now-you-see-it-testing-out-light-refraction/

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• 3 index cards
• small piece of modeling clay or sticky tack
• hole puncher
• science journal
• For each index card, use a ruler to draw lines connecting opposite corners of the card.
• At the intersection of the two lines, use a hole puncher to punch a hole in the center of the index cards.
• For each card, use a small piece of modeling clay and place the card into the clay to create a "stand" for the card. Place the cards so that they stand vertically and at an equal distance from each other. See Diagram.
• Place the flashlight at one end of the row of index cards and turn off the light in the room.
• Arrange the index cards so that light can be seen through all the holes.
• Observe and record your observations.
• How can light be seen through all the index cards?
• What does the experiment prove about the path light travels?
• What would happen if the holes were smaller?

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Light Travels Along a Straight Line

Introduction.

One type of energy that is essential to our existence is light. We are unable to envision a world without light. Light improves the beauty of everything around us and allows us to see. In both science and art, light is a crucial element. One of the crucial scientific instruments that enable scientists to examine things all across the world is light.

Some scientific theories claim that it is made up of particles, while others assert that it is made up of waves. What is the medium of propagation if the light is a wave? How does light move? We shall find answers to some of these questions in this article.

How does Light Travel?

Light can pass through a medium and in a vacuum. However, there won’t be any particles in a vacuum that light can’t reflect off of. Therefore, light is invisible in a vacuum. Light can reflect in the air when it strikes dust or other particles, making light visible in the atmosphere. Light may be thought of as having waves. Different light waves have varied wavelengths, and different light has different colours based on the wavelength. For instance, the shortest wavelength of light has a violet colour, whereas the highest wavelength of visible light has a red colour. Light, being a wave, may exhibit wave characteristics like diffraction and interference.

The answer to the question of how light typically moves is that it moves straightforwardly. However, the truth is that light’s smaller diffraction effect is the reason it appears to move in a straight line. The spreading out and the illumination of an area where a shadow is anticipated is known as diffraction, which is the bending of waves around an object. The wavelength of light is on the order of nanometers. We cannot see impediments of this size with our unaided eyes because the wavelength is too narrow. As a result, we see that light moves in a straight path. Rectilinear propagation of light is another name for the way that light moves in a straight line.

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Experiment with the Straight Line Motion of Light

Normal light travels in a straight line because there isn’t enough diffraction to cause any noticeable effects. We demonstrate that light moves in a straight line using a basic experimental setup. In front of a candle on the tabletop, arrange three cardboard sheets back to back. Ensure that the candles and cardboard sheets are arranged in a straight line. On each cardboard sheet, poke a pinhole after lighting the candle. To allow for the visibility of the candle’s flame, the holes must be made at equal heights. Now, observe which line light travels in by looking through the holes. Along the slender line of holes, the thin flame will be visible. Now move one of the cardboard sheets to either side and observe the flame. Can you see the flame? The flame won’t be seen when you move the cardboard sheet. Reposition the cardboard sheet in its original location. The flame may now be seen. The experiment diagram is shown below. From this experiment, we may infer that light moves in a straight line.

Examples of Straight-Line Motion of Light

• When a lamp, torch, or another source of light emits light, it travels in a straight line.
• When sunlight enters a dusty environment through tiny holes, a straight-line trail of light is apparent.
• The object will become invisible when an opaque object is placed in front of it. The reason for this is that an opaque object prevents light from bending through its corners.

The light rays move in a straight line. The minimized diffraction effects of light facilitate the propagation of the light in a straight path. Examples, where the light rays travel in a straight line, are the light ray that comes from a train, a torch, and/or a lamp.

Frequently Asked Questions

1. what is rectilinear propagation of light.

Ans: The motion of the light rays in a straight line is termed the rectilinear propagation of the light.

2. Explain why Light Travels in a Straight Line?

Ans: Diffraction is a wave characteristic of light. Only when the wavelength of the light wave is of the order of the dimension of the size of the particle it collides with, and the phenomena of diffraction take place. The wavelengths of light are on the order of nanometers. Typically, a nanometer-sized item is invisible to the human eye. Light’s diffraction impact is therefore too modest to be taken into account and travels in a straight-line path.

3. Why is Light Invisible in a Vacuum?

Ans: Light can travel through the vacuum, however, since there are no particles available in the vacuum, light cannot reflect in a vacuum and therefore light is invisible in a vacuum.

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• Light Travels in Straight Line

An Introduction

Light is one form of energy that plays a vital role in our life. We cannot imagine a world full of darkness. Light makes our vision possible and enhances the beauty of everything around us. Light is playing an important role in both art and science. Light is one of the important tools in science that helps scientists to observe things around the world.

Some theories of science are saying it is particles and some of them are saying light is a wave . If the light is a wave, how does light travel and what is the medium of propagation? Light travels in a straight line. The straight-line path of light is very much evident when light travels through a dusty atmosphere. In this article, we will be discussing the straight line motion of light.

How does Light Travel?

Light can travel through both in a medium and in a vacuum . But in a vacuum, there will not be any particles light can not reflect by hitting it. Hence, in a vacuum, light is invisible. In air, light can be reflected by hitting dust or some other particles, hence light is visible in the air.

Light can be considered as waves. Light waves travel in different wavelengths and depending on the wavelength, different light has different colours. For example, the high wavelength light in visible light has a red colour and the shortest wavelength of light has a violet colour. Being a wave light can show properties of waves such as interference and diffraction .

The answer to the question of how light normally travels is that light travels in a straight line. But the actual answer is light seems to travel in a straight line because of the smaller diffraction effect of light. Diffraction is the bending of waves around an object such that it spreads out and illuminates an area where a shadow is expected.

For light, the wavelength is in the order of nanometers. This wavelength is too small and obstacles of this size cannot be determined by our naked eyes. Hence, we feel that light travels along a straight line. The straight-line motion of light is also called rectilinear propagation of light .

Experiment for the Straight Line Motion of Light

Since the diffraction effect of light is too small, normally light travels along a straight line. By using a simple experimental setup, we can prove that light travels along a straight line.

Place three cardboard sheets back to back in front of a candle on the tabletop. Make sure that the cardboard sheets and the candles are placed in a straight line. Light the candle and make a pinhole on each cardboard sheet. The holes should be made at equal height such that the flame of the candle is visible through them. Now look through the holes and observe light travels in which line. The light flame will be visible along the straight line of holes. Now move one of the cardboard sheets to either side and observe the flame. Can you see the flame? On moving the cardboard sheet, the flame will not be visible. Now, again place the cardboard sheet back in its position. The flame is visible now.

From this experiment, we can conclude that light travels along a straight line and this experiment diagram is given below.

Examples of Straight Line Motion of Light

Light travels in straight line examples are as follows:.

Light comes out from a torch or train or lamp follows a straight line path.

A straight line path of light is visible when Sunlight comes out through the small holes in a dusty atmosphere.

When we place any opaque object in front of the object, we observe that the object will be invisible. It is because light cannot bend through the corners of the opaque object.

Interesting Facts

Sunlight can reach a depth of 80m in the ocean.

Paul Dirac proposed a theory in explaining the dual nature of light in 1927.

Particles of light are called photons.

The scientist Euclid Catoptrics in 280 BC found light travels in straight-line inhomogeneous media.

Key Features

Light travels along a straight line.

The straight-line motion of light is due to its small diffraction effects.

Light comes out from the train, torch, and lamp are examples of straight line motion of light.

FAQs on Light Travels in Straight Line

1. What is rectilinear propagation of light?

Light travels along a straight line. The straight-line motion of light is called rectilinear propagation of light.

2. Explain why light travels in a straight line?

Light is a wave exhibiting the property of diffraction. The phenomenon of diffraction is observed only if the wavelength of the wave matches the size of the particle it collides with. Light has wavelengths in the order of nanometers. Usually, an object of nanometer size can not be seen by the naked eye. Hence, the diffraction effect of light is too small to be considered. So, light appears to travel along a straight line.

3. Why is light invisible in a vacuum?

Light can travel through a vacuum. Since in a vacuum there are no particles, light can not reflect. Hence, light is invisible in a vacuum.

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Light Travels in Straight Lines — Experiments (Year 6)

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Help children to learn about how light travels with this worksheet. It includes two different experiments that demonstrate how light travels in a straight lines, even when reflected. Detailed instructions and diagrams are provided.

• Key Stage: Key Stage 2
• Subject: Science
• Topic: Light
• Topic Group: Physical Processes
• Year(s): Year 6
• Media Type: PDF
• Resource Type: Activities & Games
• Last Updated: 25/10/2023
• Resource Code: S2WAC1725
• Curriculum Point(s): Recognise that light appears to travel in straight lines.

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How light travels

I can explain that light travels in straight lines.

Lesson details

Key learning points.

• We need light to be able to see things.
• Light travels out from a source of light in all directions.
• Light travels in straight lines.
• Scientists use diagrams to show light travelling in straight lines .

Common misconception

When children think of light, they do not necessarily think of it as travelling. Also that light is found only in bright areas and not in the space between.

Provide opportunities for children to think of different ways to model and record travelling light so it is seen as a continuous straight line.

Light - We can detect with our eyes in order to see things.

Light source - Something that is a light source produces its own light.

Record - To record information is to keep it so that it can be passed on to others. This can be done in many ways including notes, tables, photos and drawings.

Diagram - A diagram is a simplified drawing of information.

Torches, thick card (some pre-cut with holes in the centre) and string.

Content guidance

• Risk assessment required - equipment
• Exploration of objects

Supervision

Adult supervision required

This content is © Oak National Academy Limited ( 2024 ), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Starter quiz

6 questions.

light cannot pass through it

translucent -  

lets some light through but is not completely see-through

transparent -  

lets light pass through and is completely see-through

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Year 6: Light

This list consists of lesson plans, activities and video clips to support the teaching of light in year six. It contains tips on using the resources, suggestions for further use and background subject knowledge. Possible misconceptions are highlighted, so that teachers may plan lessons to facilitate correct conceptual understanding. Designed to support the new curriculum programme of study it aims to cover many of the requirements for knowledge and understanding and working scientifically. The statutory requirements are that children are taught to:

· recognise that light appears to travel in straight lines · use the idea that light travels in straight lines to explain that objects are seen because they give out or reflect light into the eye · explain that we see things because light travels from light sources to our eyes or from   light sources to objects and then to our eyes · use the idea that light travels in straight lines to explain why shadows have the same shape as the objects that cast them.

Visit the primary science webpage to access all lists.  

Modelling Light

Quality Assured Category: Science Publisher: Teachers TV

This video is a way of helping children understand that light travels in a straight line from a light source, reflects off an object, a mirror and then into the eye. This is modelled using a torch, teddy, mirror and ribbon to represent the light. The teacher discusses how modelling can address misconceptions and help children access an abstract concept. Working in groups children could then build their own model and draw what is happening on a large sheet of paper.

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Contains a presentation which shows different sources of light, an activity which explores how we need light to see, sources of light, how we see objects, reflection of light and the composition of white light. The presentation is interspersed with class experiments, games and activities. The teachers' notes deal with the common misconceptions around light and show how the presentation and activities help address them.

Light: crime lab investigation

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Session B helps children develop their understanding that light travels in straight lines and can be blocked by opaque objects. Allow children to design a test to see if different materials block light and produce shadows and if the resulting shadows differ depending on the material used. Include some translucent and transparent materials and note observations. A shadow is usually black because it is an absence of light however a coloured filter may change the shadow e.g. a red filter will let red light pass through it to produce a red shadow as the other colours of the spectrum are absorbed.

Making Shadows

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This template and instructions can be used to create periscopes. Children may then explore how they work and explain this.

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What factors affect the size of a shadow in a shadow theatre?

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The magic of light

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Make your own spectroscopes and colour wheel to study the properties of light.

Year 6 - Starters for Science* Suitable for Home Learning*

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Light travels in straight lines

A KS2 PowerPoint of experiment ideas for teaching the concept that light travels in straight lines and can be reflected using mirrors.

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NOTIFICATIONS

Light basics.

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Light is a form of energy produced by a light source. Light is made of photons that travel very fast. Photons of light behave like both waves and particles.

Light sources

Something that produces light is called a light source. There are two main kinds of light sources:

Fireworks show how light travels faster than sound. We see the light almost instantly, but the sound arrives later. To work out how many kilometres away the fireworks are, count the seconds until you hear the bang and divide by 3.

Incandescent sources use heat to produce light. Nearly all solids, liquids and gases will start to glow with a dull red colour once they reach a temperature of about 525 °C. At about 2300 °C, the filament in a light bulb will start to produce all of the colours of the visible spectrum, so it will look white. The Sun, stars, a flame and molten metal are all incandescent.

Luminescent sources are normally cooler and can be produced by chemical reactions, such as in a glowstick or a glow-worm. Other luminescent sources include a computer screen, fluorescent lights and LEDs.

Light travels much faster than sound

Light travels at a speed of 299,792,458 m/s (that’s nearly 300,000 km/s!). The distance around the Earth is 40,000 km, so in 1 second, light could travel seven and a half times around the world.

Sound only travels at about 330 m/s through the air, so light is nearly a million times faster than sound.

If lightning flashes 1 kilometre away from you, the light reaches you in 3 millionths of a second, which is almost instantly. The sound of the thunder takes 3 seconds to travel 1 kilometre – to work out many kilometres away lightning is, count the seconds for the thunder to arrive and divide by 3.

Lightning storms are important for converting nitrogen gas in the atmosphere through to forms that are biologically available.

Light takes about 8 minutes and 20 seconds to reach the Earth from the Sun. When we see the Sun, we are seeing what it looked like over 8 minutes ago.

Light can travel through empty space

Unlike sound, which needs a medium (like air or water) to travel through, light can travel in the vacuum of space.

Light travels in straight lines

Once light has been produced, it will keep travelling in a straight line until it hits something else.

Shadows are evidence of light travelling in straight lines. An object blocks light so that it can’t reach the surface where we see the shadow. Light fills up all of the space before it hits the object, but the whole region between the object and the surface is in shadow. Shadows don’t appear totally dark because there is still some light reaching the surface that has been reflected off other objects.

Once light has hit another surface or particles, it is then absorbed, reflected (bounces off), scattered (bounces off in all directions), refracted (direction and speed changes) or transmitted (passes straight through).

Models for light

Wave length, height and frequency

A wave can be described by its length, height (amplitude) and frequency.

Light as waves

Rainbows and prisms can split white light up into different colours. Experiments can be used to show that each of these colours has a different wavelength.

When white light shines through a prism, each colour refracts at a slightly different angle. Violet light refracts slightly more than red light. A prism can be used to show the seven colours of the spectrum that make up white light.

At the beach, the wavelength of water waves might be measured in metres, but the wavelength of light is measured in nanometres – 10 -9 (0.000,000,001) of a metre. Red light has a wavelength of nearly 700 nm (that’s 7 ten-thousandths of a millimetre) while violet light is only 400 nm (4 ten-thousandths of a millimetre).

Visible light is only a very small part of the electromagnetic spectrum – it’s just that this is the range of wavelengths our eyes can detect.

Light as particles

In 1905, Albert Einstein proposed that light is made of billions of small packets of energy that we now call photons. These photons have no mass, but each photon has a specific amount of energy that depends on its frequency (number of vibrations per second). Each photon still has a wavelength. Shorter wavelength photons have more energy.

The photoelectric effect

University of Waikato science researcher Dr Adrian Dorrington explains the photoelectric effect. He then describes how camera sensors can be designed on the basis of this effect to enable light energy to be converted into electric potential energy.

The photoelectric effect is when light can cause electrons to jump out of a metal. These experiments confirm that light is made of these massless particles called photons.

Simple explanations of some of these concepts can be found in the article Building Science Concepts: Shadows .

Nature of science

In order to understand the world we live in, scientists often use models. Sometimes, several models are needed to explain the properties and behaviours of a phenomenon. For example, to understand the behaviour of light, two models are needed. Light needs to be thought of as both waves and particles.

Useful links

Even though light doesn’t have mass, learn how it still has a tiny amount of momentum. Find out about NASA’s solar sails to power spacecraft.

Read about the LightSail project, a crowdfunded project from The Planetary Society, aiming to demonstrate that solar sailing is a viable means of propulsion for CubeSats (miniature satellites intended for low Earth orbit).

Explore solar sails more in your classroom, with this activity Solar Sails: The Future of Space Travel from the TeachEngineering website.

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