Test: Ray Optics - 1 - Class 10 MCQ

The image in a plane mirror forms virtual and erect image and appears to be as far behind the mirror as the object is in front of the mirror. A diverging lens or a convex mirror forms a virtual image.A virtual image is produced by a concave mirror when the object is placed inside the focal length of the mirror.

Angle of Incidence:

The angle of incidence is the angle between the normal to the surface and the incident ray.

The incident ray is the ray of light that strikes the surface of the mirror.

The normal to the surface is an imaginary line perpendicular to the surface of the mirror at the point of incidence.

Therefore, the angle of incidence is the angle between the incident ray and the normal to the surface of the mirror.

Angle of reflection is the angle between a reflected ray and the normal drawn at the point of incidence to a reflecting surface.

When the object is placed at the center of curvature, the image is formed at the center of curvature and we know that the relation between radius of curvature and focal length is R= 2F ( R is used to show radius of curvature And F is the focal length ) if you will notice the its ray diagram then u could see that radius of curvature is always twice of Focal length.

The size of the image will  be 2.0 cm.
V=U(given)
m=-v/u
m= - 1
m=h`/h
-1=h`/2
h`=-2
h=2cm

For spherical mirrors,

m = - v/u

‘m’ is negative when both ‘v’ and ‘u’ have negative values. That is both object and image are on the same side.

So, the correct option is d. The image is inverted, since, it is real.

Option ( a) is the correct answer. As the object is always placed on the left side of the mirror and according to the sign convention, it has negative value for 'so axis.

Therefore, spherical mirrors have only one reflecting surface and it will be negative only.

The relation f = R/2 is applicable only for mirrors. For lenses, you have to use the lens makers formula.

Reflection of a ray of light on a concave mirror
When a ray of light is incident on a concave mirror parallel to the principal axis, it will follow the laws of reflection.

The ray of light will be reflected such that it passes through the focus of the concave mirror.

This is because the focus is the point on the principal axis where rays of light parallel to the axis converge after reflection.

Therefore, the correct answer is A: pass through the focus.

An incident ray which passes through the centre of curvature C of the mirror is reflected back along it's own path ( since it is normally incident on the mirror) .

A convex mirror never forms an image larger than the original object, whereas a concave mirror can form an image larger than the object between the centre of curvature and the point of focus.

The light ray bends towards the normal as it travels from a rarer medium of air to a denser medium of water, under goes refraction. Refraction is due to change in the speed of light as it enters from one transparent medium to another. The speed of light increases in rarer medium and decreases in denser medium.

Refractive index, also called index of refraction, measure  of the bending of a ray of light when passing from one medium into another. As per Snell's law and the given information ;

According to sign convention distances and points are given their positive or negative sign on the basis of direction of propagation of incident Ray and the focus of both convex mirror and lens are in the front of propagating incident Ray of light so it is taken as positive.

Explanation:

Convex lens A: is thicker at the middle than at the edges

Convex lenses are thicker at the center and thinner towards the edges.

This shape causes light rays passing through the lens to converge or come together at a focal point.

This property makes convex lenses useful for focusing light in applications such as cameras, eyeglasses, and projectors.

A virtual image of an object is formed by a convex lens only when the object is placed between the lens and the focus. Therefore, the focal length of the lens should be greater than the distance of the object from the lens. 

Convex Lens: A convex lens is thicker at the center and thinner at the edges. When light rays pass through a convex lens, they converge at a point called the focal point.

Image Formation: When an object is placed before a convex lens, the light rays from the object refract through the lens and form an image on the other side. The image formation by a convex lens depends on the distance of the object from the lens.

Real or Virtual Image: The image formed by a convex lens can be real or virtual, depending on the position of the object relative to the lens.

Real Image: A real image is formed when the light rays actually converge at a point after passing through the lens. This real image can be projected onto a screen and is always inverted.

• Virtual Image: A virtual image is formed when the light rays appear to converge at a point on the same side of the lens as the object. This virtual image cannot be projected onto a screen and is always upright.
• Conclusion: Therefore, when an object is placed before a convex lens, the image formed may be real or virtual, depending on the position of the object relative to the lens.

Because concave  lens always produce an
Image which is always erect, diminished and virtual.
 

1/f = (n - 1) ×  (1/R2)

1/f = (1.5 - 1) × (1/20)

1/f = 0.025

f = 1/0.025

f = 40 cm

Therefore, the focal length of the plano-convex lens is 40 cm.

Concave mirror and magnification: A concave mirror can produce both real and virtual images. The magnification produced by a concave mirror can be positive or negative depending on the position of the object relative to the mirror.

Negative magnification: In the case of a negative magnification, the image formed is inverted compared to the object. Negative magnification indicates a reduction in size.

Mirror formula: The magnification produced by a concave mirror is given by the formula M = -v/u, where M is the magnification, v is the image distance, and u is the object distance.

Placing the object: In order to obtain a magnification of -0.6 with a concave mirror, the object must be placed beyond the center of curvature. This is because the magnification is negative, indicating an inverted image, and the object distance should be greater than the image distance.

Position of the object: Placing the object beyond the center of curvature ensures that the image distance is greater than the object distance, resulting in a negative magnification value as required.

The Laws of Reflection for Mirrors

- The laws of reflection apply to all mirrors, regardless of their shape.
- These laws state that the angle of incidence is equal to the angle of reflection.
- This means that the light rays that strike the mirror are reflected at the same angle.
- Whether the mirror is concave, convex, or plane, these laws will always hold true.
- Therefore, option B is correct as it includes all mirrors, not just a specific type.

A transparent medium is a material that allows light to pass through.

When light encounters a transparent medium, it can penetrate the material and transmit through it.

Examples of transparent mediums include glass, water, and air.

Transparent mediums are essential for various applications such as optics, windows, and lens.

Explanation:

- Magnification produced by a rear view mirror in vehicles is less than one: Rear view mirrors in vehicles are designed to provide a wider field of view to the driver. This means that objects appear smaller in the mirror compared to their actual size.

- Convex shape: Rear view mirrors are typically convex in shape, which causes objects to appear smaller and farther away than they actually are. This helps in reducing blind spots and improving visibility for the driver.

- Reduced size of objects: The convex shape of the mirror causes light rays to diverge, resulting in a reduced size of objects being reflected in the mirror. This reduction in size is what causes the magnification to be less than one.

- Importance of magnification less than one: Having a magnification less than one is important in rear view mirrors as it allows the driver to see a wider area behind the vehicle without the need to constantly adjust the mirror. This helps in improving safety on the road by reducing blind spots and providing a better overall view of the surroundings.

Explanation:

- Mirror A is concave: Concave mirrors converge light rays to a focal point, creating an enlarged image.
- Mirror B is plane: Plane mirrors reflect light without any distortion, creating an image the same size as the object.
- When the man moves towards the mirrors, the concave mirror A enlarges his face while the plane mirror B keeps the size the same.