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Light - Spherical Mirrors: Concave and Convex

Grade 7CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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A spherical mirror is a mirror whose reflecting surface is a part of a hollow sphere of glass.

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A Concave Mirror has a reflecting surface that is curved inwards. It is also known as a converging mirror because it bends light rays towards a single point called the focus (FF).

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A Convex Mirror has a reflecting surface that is curved outwards. It is also known as a diverging mirror because it spreads out light rays.

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The center of the reflecting surface of a spherical mirror is called the Pole (PP).

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The center of the sphere of which the mirror is a part is called the Center of Curvature (CC).

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The distance between the Pole (PP) and the Principal Focus (FF) is called the Focal Length (ff).

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A Real Image is an image that can be obtained on a screen. Concave mirrors can form real images when the object is placed beyond the focus.

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A Virtual Image is an image that cannot be obtained on a screen. Convex mirrors always form virtual, erect, and diminished images.

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Concave mirrors are used by dentists to see enlarged images of teeth and in torch reflectors. Convex mirrors are used as side-view mirrors in vehicles because they provide a wider field of view.

📐Formulae

R=2fR = 2f

f=R2f = \frac{R}{2}

where R=Radius of Curvature and f=Focal Length\text{where } R = \text{Radius of Curvature and } f = \text{Focal Length}

💡Examples

Problem 1:

If the radius of curvature (RR) of a spherical mirror is 30 cm30 \text{ cm}, what is its focal length (ff)?

Solution:

Given R=30 cmR = 30 \text{ cm}. Using the formula f=R2f = \frac{R}{2}, we get f=302=15 cmf = \frac{30}{2} = 15 \text{ cm}.

Explanation:

The focal length of a spherical mirror is always half of its radius of curvature.

Problem 2:

An object is placed very close to a concave mirror. Describe the nature of the image formed.

Solution:

The image will be Virtual, Erect, and Magnified (larger than the object).

Explanation:

In a concave mirror, when the object is placed between the Pole (PP) and the Focus (FF), the reflected rays appear to diverge from behind the mirror, forming a virtual and enlarged image.

Problem 3:

Why are convex mirrors preferred as rear-view mirrors in cars?

Solution:

Convex mirrors always form an erect and diminished image, which allows the driver to see a much larger area of traffic behind them.

Explanation:

Because convex mirrors curve outwards, they have a wider field of view compared to plane or concave mirrors.