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Q1. Apparent displacement is due to: Physics
Apparent displacement occurs when light bends as it passes from one medium to another. This bending (refraction) makes objects appear shifted from their actual position. For example, a pencil in water appears bent due to refraction of light.
Q2. The phenomenon by which light bends between media is called
Refraction is the bending of light when it passes obliquely from one transparent medium to another. This happens because the speed of light changes in different media. Reflection is bouncing back, while dispersion is splitting of light into colors.
Q3. The mirror that gives an erect and enlarged image is
A concave mirror gives an erect and enlarged (magnified) image when the object is placed between the focus and the pole. This is why concave mirrors are used as shaving mirrors and makeup mirrors. Convex mirrors give diminished images.
Q4. The principal axis is taken as
In the Cartesian sign convention for mirrors and lenses, the principal axis is taken as the x-axis. All distances are measured along this axis from the pole (origin). The y-axis is used for measuring heights of objects and images.
Q5. The distance from pole to focused point is known as
Focal length (f) is the distance between the pole (P) and the focus (F) of a spherical mirror. It is half of the radius of curvature. The image distance is the distance from the pole to the image.
Q6. The image formed by a convex mirror is always
A convex mirror always forms a virtual, erect, and diminished (smaller) image regardless of the object’s position. This is why convex mirrors are used in vehicles to provide a wider field of view, even though objects appear smaller.
Q7. The distance between image and pole is called
Image distance (v) is the distance between the image and the pole of the mirror. Object distance (u) is the distance between the object and the pole. Focal length (f) is the distance between the pole and the focus.
Q8. Refraction proves that light does not move
Refraction proves that light does not always travel in a straight line. When light enters a different medium, it bends and changes direction. Light travels in a straight line only in a single homogeneous medium.
Q9. A convex mirror always forms an image that is
A convex mirror always forms a virtual and erect image. The image is also diminished (smaller). It is formed behind the mirror and cannot be obtained on a screen. This is a unique property of convex mirrors.
Q10. The distance between object and pole is called
Object distance (u) is the distance between the object and the pole of the mirror. It is always taken as negative according to the sign convention because the object is placed on the same side as the incident light.
Q11. Light travels in straight line only in
Light travels in a straight line only in a single homogeneous medium. When it moves from one medium to another, its speed changes and it bends (refraction). In vacuum, it travels straight, but the key is that it remains in the same medium.
Q12. Refraction shows that speed of light
Refraction occurs because light travels at different speeds in different media. Light is fastest in a vacuum and slows down in materials like water, glass, and diamond. This change in speed causes the light to bend.
Q13. Refraction occurs when light travels
Refraction occurs only when light passes from one transparent medium to another. At the boundary between the two media, the speed of light changes, causing it to bend. In a single medium, light travels in a straight line without bending.
Q14. The formula that relates u, v, and f is called
The mirror formula is 1/v + 1/u = 1/f, where u is the object distance, v is the image distance, and f is the focal length. This formula applies to all spherical mirrors and is fundamental in solving mirror problems.
Q15. Convex mirrors are used as rear-view mirrors in vehicles because they
Convex mirrors give erect and diminished images. They also provide a wider field of view. Although objects appear smaller and farther away, the driver can see a larger area behind the vehicle, making driving safer.
Q16. The apparent rising of the bottom of a pond is due to
The bottom of a pond appears raised because light from the bottom travels from water (denser) to air (rarer) and bends away from the normal. Our brain interprets this as the bottom being shallower than it actually is.
Q17. Letter appears raised under glass because light
When light passes through a glass slab placed over a letter, it refracts twice—once entering and once leaving the glass. This causes the light to change direction, making the letter appear raised from its actual position.
Q18. Distances measured below the principal axis are
According to the sign convention, distances measured below the principal axis (downward) are taken as negative. Distances measured above the principal axis (upward) are taken as positive. This applies to the heights of images and objects.
Q19. A lemon kept in water appears bigger because of
A lemon in water appears bigger because light rays from the lemon bend as they pass from water to air. The curved glass of the container also acts like a lens. This refraction makes the lemon appear larger than its actual size.
Q20. Height of real image is taken as
According to the sign convention, the height of a real image is taken as negative because real images are always inverted (formed below the principal axis). Virtual images have positive height because they are erect (formed above the principal axis).
Q21. Light changes its path when it enters a new medium because of
Light changes its path when it enters a new medium due to refraction. This happens because the speed of light changes in different media. The change in speed causes the light to bend at the boundary between the two media.
Q22. Negative value of magnification indicates image is
A negative magnification means the image is real and inverted. A positive magnification means the image is virtual and erect. Magnification tells us about the orientation of the image, not its size or brightness.
Q23. Distances measured above the principal axis are
According to the sign convention, distances measured above the principal axis (upward) are taken as positive. This applies to the heights of erect images and objects. Distances below the principal axis are negative.
Q24. Magnification is defined as the ratio of
Magnification (m) is the ratio of the height of the image (hᵢ) to the height of the object (h₀). So, m = hᵢ/h₀. It can also be calculated as m = -v/u for mirrors, but the basic definition is the ratio of heights.
Q25. If water is replaced by kerosene, the bending will be
Different media have different refractive indices. Kerosene has a different refractive index than water. Therefore, the amount of bending (refraction) will be different when light passes between air and kerosene compared to air and water.
Q26. When light enters another medium it generally
When light enters another medium obliquely, it generally changes direction due to refraction. The change in speed causes the light to bend. If it enters along the normal, it does not change direction but still changes speed.
Q27. According to sign convention, the object is always placed
According to the Cartesian sign convention, the object is always placed to the left of the mirror (on the same side as the incident light). Therefore, the object distance (u) is always negative for real objects.
Q28. A convex mirror allows the driver to view
Convex mirrors provide a wider field of view. They allow the driver to see a larger area behind the vehicle, including vehicles in adjacent lanes. This is why they are preferred as rear-view mirrors.
Q29. The field of view in a convex mirror is
Convex mirrors have a wider field of view than plane mirrors because they bulge outward and reflect light from a larger area. This is the main reason they are used in vehicles and for security purposes.
Q30. The focal length of a mirror with radius of curvature 20 cm is
The focal length (f) is half of the radius of curvature (R). So, f = R/2 = 20/2 = 10 cm. This relationship (f = R/2) is true for all spherical mirrors, whether concave or convex.
Q31. Height of object is always taken as
The height of the object is always taken as positive according to the sign convention. This is because objects are always placed erect (upright) above the principal axis. Only the height of the image can be positive or negative.
Q32. The mirror formula is valid for
The mirror formula 1/v + 1/u = 1/f is valid for all spherical mirrors—both concave and convex—provided the proper sign convention is applied. It is not valid for plane mirrors (which have infinite focal length).
Q33. A pencil immersed in water appears bent because
When a pencil is immersed in water, light from the submerged part bends as it travels from water to air. This refraction makes the pencil appear bent or broken at the water surface. This is a common example of refraction in daily life.
Q34. A glass slab changes direction of light because of
When light passes through a glass slab, it refracts twice—once when entering the glass and once when leaving it. This causes a lateral shift in the light’s path. The direction changes due to the change in speed of light in glass.
Q35. Distances measured to the left are considered
According to the sign convention, distances measured to the left of the mirror (opposite to the direction of incident light) are considered negative. This is why object distance (u) is always negative for real objects.
Q36. Light leaving water into air will
Light travels slower in water (denser medium) than in air (rarer medium). When light leaves water and enters air, its speed increases. This change in speed causes the light to bend away from the normal.
Q37. The extent of bending depends on
The extent of bending (refraction) depends primarily on the refractive index of the medium, which is a property of the medium. Different media have different refractive indices, so light bends differently in different media.
Q38. Apparent depth is different from real depth due to
The apparent depth of a liquid is different from its real depth because of refraction. Light from the bottom of the liquid bends at the surface, making the bottom appear shallower than it actually is. This is why a swimming pool looks less deep than it really is.
Q39. Light entering water from air will
Light travels faster in air (rarer medium) than in water (denser medium). When light enters water from air, it slows down. This slowing down causes the light to bend towards the normal.
Q40. Positive magnification indicates image is
Positive magnification means the image is virtual and erect (upright). This happens when the image is formed on the same side as the object. Negative magnification indicates a real and inverted image.
Q41. Distances measured to the right are considered
According to the sign convention, distances measured to the right of the mirror (in the direction of incident light) are considered positive. This applies to image distance (v) when the image is real and formed on the same side as the object.
Q42. The principal focus of a concave mirror is the point where
The principal focus (F) of a concave mirror is the point on the principal axis where parallel rays of light converge after reflection from the mirror. This is why concave mirrors are called converging mirrors.
Q43. Height of virtual image is taken as
Virtual images are always erect (upright). According to the sign convention, the height of an erect image is taken as positive. Therefore, the height of a virtual image is positive.
Q44. Refraction is caused by change in
Refraction is caused by a change in the speed of light when it enters a different medium. This change in speed causes the light to bend (change direction). The frequency of light remains constant during refraction.
Q45. The purpose of using convex mirrors in vehicles is
Convex mirrors are used in vehicles to provide a wider field of view, allowing the driver to see more of the road behind. This helps in safe driving by reducing blind spots and helping the driver avoid accidents.
Q46. Optical density affects
Optical density determines how much light slows down in a medium. This affects the path of light—when light enters a medium of different optical density, it bends (refraction). Higher optical density means more bending.
Q47. Convex mirrors are curved
Convex mirrors have a reflecting surface that bulges outward (like the outside of a spoon). This outward curvature causes the mirror to diverge light and form virtual, erect, and diminished images.
Q48. The symbol generally used for magnification is
The symbol for magnification is ‘m’. It represents the ratio of the height of the image to the height of the object. Other symbols include f for focal length, v for image distance, and u for object distance.
Q49. The pole of a spherical mirror is taken as
In the sign convention, the pole (P) of the spherical mirror is taken as the origin (0,0). All distances are measured from this point along the principal axis. Distances to the left are negative, and to the right are positive.
Q50. The raised appearance of letters under glass slab is due to
When a glass slab is placed over a letter, light from the letter refracts through the glass. The bending of light makes the letter appear raised from its actual position. This is another example of refraction in daily life.