Light MCQ & Questions — Free Practice with Answers
Free light MCQ questions with answers, based on analysis of past PSLE papers, MOE syllabus requirements, and common exam mistakes.
- Taught in Primary 4 under the Energy theme in the MOE syllabus
- Shadows and light sources are commonly tested in PSLE Booklet A (MCQ)
- 2024 PSLE trend: application questions combining light with everyday scenarios
Key Concepts
Sources of light
There are two types of light sources. Natural sources include the Sun, stars, and fireflies — they produce their own light. Artificial sources are made by people, such as light bulbs, torches, and candles. Objects that produce their own light are called luminous objects.
How we see objects
We can see an object in two ways. If the object is a light source (like a torch), it sends light directly to our eyes. If the object is not a light source (like a book), light from a source must first hit the object, bounce off it, and then enter our eyes. This is why we cannot see objects in complete darkness.
Light travels in straight lines
Light always travels in straight lines. It cannot bend around corners or curve around objects. A simple experiment proves this: line up three cards with holes in a row. You can only see a candle flame through all three holes when they are perfectly aligned — move one card sideways, and you can no longer see the flame.
How shadows are formed
A shadow is formed when light is blocked by an object. Because light travels in straight lines, it cannot go around the object. Three things are needed to form a shadow: a light source, an object to block the light, and a surface (screen) for the shadow to fall on.
Variables affecting shadows
Several factors change the size, shape, and position of a shadow:
- Distance between light source and object: Moving the object closer to the light source makes the shadow larger. Moving it further away makes the shadow smaller. (Memory aid: NLB — Near Light, Bigger.)
- Distance between object and screen: Moving the object closer to the screen makes the shadow smaller. Moving it further away makes the shadow larger. (Memory aid: NSS — Near Screen, Smaller.)
- Shape and position of the object: The shadow takes on the outline shape of the object as seen from the direction of the light. Rotating the object changes the shadow's shape.
Key Terms for PSLE
- Light source
- An object that produces its own light. Examples include the Sun, a lighted torch, and a burning candle. Also called a luminous object.
- Luminous object
- An object that gives off its own light. The Sun and a lighted bulb are luminous. They can be seen because light travels directly from them to our eyes.
- Non-luminous object
- An object that does not produce its own light. A book, a wall, and the Moon are non-luminous. We can see them only when light from a source bounces off them and enters our eyes.
- Shadow
- A dark area formed on a surface when an object blocks light from reaching that area. The shadow takes the outline shape of the object blocking the light.
- Reflect
- When light bounces off the surface of an object. Non-luminous objects can be seen because they reflect light into our eyes.
Common Misconceptions
We reviewed PSLE marking schemes and student answer scripts to identify the mistakes that cost marks most often.
“Light can bend around corners.” Light always travels in straight lines. It cannot bend around objects or corners. This is precisely why shadows form — the light cannot curve around the object to reach the area behind it.
“Shadows are always the same size as the object.” The size of a shadow depends on the distance between the object and the light source, and the distance between the object and the screen. Shadows are only the same size as the object under very specific conditions.
“The Moon is a source of light.” The Moon is a non-luminous object — it does not produce its own light. It appears bright because it reflects light from the Sun. Only objects that produce their own light are light sources.
“The colour of a shadow depends on the colour of the object.” A shadow is always dark, regardless of the colour of the object blocking the light. Shadows are simply areas with less light. A red ball and a blue ball of the same size in the same position will produce identical shadows.
Practice Questions
Practice light questions with answers below — great for revision. Each question is modelled on common PSLE patterns for light and shadows, with a detailed explanation covering why wrong answers are wrong — not just the right one.
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