Class 7 Science - PUNJAB
Light: Shadows and Reflections
The Class 7 PSEB chapter 'Light: Shadows and Reflections' introduces students to the fascinating behavior of light. It covers how light travels in a straight line, what luminous and non-luminous objects are, and the conditions necessary for forming shadows. Students will learn about transparent, translucent, and opaque materials, and how mirrors change the direction of light through reflection. This chapter forms the foundation of optics and is very important for Punjab Board exams, frequently featuring in both objective and descriptive questions.
Start Learning FreeKey Concepts
Rectilinear Propagation of Light
Light travels along a straight-line path, which is why we cannot see around sharp corners or through bent tubes.
Transparent, Translucent, and Opaque Objects
Transparent objects let light pass through clearly, translucent objects let some light pass through partially, and opaque objects do not let any light pass through.
Shadow Formation
A dark patch formed when an opaque object blocks the path of light; it requires a source of light, an opaque object, and a screen.
Reflection of Light
The bouncing back of light rays from a smooth, shining surface like a plane mirror, which allows us to see images.
Lateral Inversion
The phenomenon where the right side of an object appears as the left side, and vice versa, when seen in a plane mirror.
Important Formulas
Board Exam Info
In Punjab (PSEB) Class 7 Science exams, this chapter typically carries around 4 to 6 marks. Common question types include fill-in-the-blanks, true/false, definition-based questions (like defining shadows or reflection), and short-answer questions explaining why shadows are formed or describing lateral inversion.
Frequently Asked Questions
Why is a shadow always black even if the object is colored?
A shadow is simply an absence of light. When an opaque object blocks light, no light reaches the screen from that region, creating a dark patch regardless of the object's color.
What is the difference between a transparent and a translucent material?
Transparent materials (like clear glass) allow almost all light to pass through them so objects can be seen clearly. Translucent materials (like butter paper) allow only some light to pass, making the view blurred.
Why do letters of the word 'AMBULANCE' appear inverted on the vehicle?
They are written with lateral inversion so that drivers of vehicles ahead can read the word correctly in their rear-view mirrors and give way quickly.
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