PREBOARD EXAMINATION 2020-21 (ONLINE BASED)
Class: 10th
SCIENCE
NOTE- All questions are compulsory.
1) Electrical resistivity of any given metallic wire depends upon
(a) its thickness
(b) its shape
(C) nature of the material
(d) its length
2)What is the commercial unit of electrical energy?
(a) Joules
(b) Kilojoules
(C) Kilowatt-hour
(d) Watt-hour
3)Inside the magnet, the field lines moves
(a) from north to south
(C) away from south pole
(b) from south the north
(d) away from north pole
4)By which instrument, the presence of magnetic field be determined?
(a) Magnetic Needle
(b) Ammeter
(C) Galvanometer
(d) Voltmeter
5) The angle of incidence for a ray of light having 30^ reflection angle is
(a) o
(b) 30°
(C) 45°
(d) 90°
6)Which of the following mirror is used by a dentist to examine a small cavity?
(a) Convex mirror
(b) Plane mirror
(c) Concave mirror
(d) Combination of convex and concave mi
7)Light from the Sun falling on a convex lens will converge at a point called
(a) centre of curvature
(b) focus
(c) radius of curvature
(d) optical centre
8)A divergent lens will produce
(a) always real image
(c) both real and virtual image
(b) always virtual image
(d) none of these
9) The muscular diaphragm that controls the size of the pupil is
(a) cornea
(b) ciliary muscles
(c) iris
(d) retina
10) Near and far points of a young person normal eye respectively are
(a) 0 and infinity
(b) 0 and 25 cm
(c) 25 cm and infinity
(d) 25 cm and 150 cm
11) The image formed on the retina of the human eye is
(a) virtual and inverted
(b) real and inverted
(c) real and erect
(d) virtual and erect
12) Refraction of light by the earth's atmosphere due to variation in air density is called
(a) atmospheric reflection
(b) atmospheric dispersion
(c) atmospheric scattering
(d) atmospheric refraction
Answers
1) Electrical resistivity of a given metallic wire depends on number density of free electrons in the conductor which is the nature of material, i.e., number of free electrons per unit volume. It also depends on the temperature of conductor.
2) kWh
Answer: The commercial unit of electrical energy is a kilowatt-hour (kWh).
3) Magnetic field lines are the lines surrounding a magnet which emerge from the north pole and terminate at the south pole, outside the magnet. ... Inside the magnet however, these lines tend to move from south pole towards north pole. They are almost parallel to each other inside the magnet.
4) A compass can be used to detect presence of magnetic field as it will deflect from its N-S direction to direction if magnetic field at that point.
6) Since, the concave mirror forms a virtual, erect but magnified image of the object when the object is placed at a distance smaller than focal length of mirror. So dentists use concave mirror to examine small cavity.
7) Light from the Sun falling on convex lens will converge at a point called as principal focus.
8) A diverging lens is a lens which always diverges rays of light incident on the lens parallel to the principal axis. ... Therefore, the divergent lens will always produce a virtual image.
9) Iris: Iris is a structure behind the cornea. It is a dark muscular diaphragm that controls the size of the pupil. The pupil regulates and controls the amount of light entering into the eye.
10) Step by step solution by experts to help you in doubt clearance & scoring excellent marks in exams. The far point of human eye with normal vision is at infinity and the near point is at a distance of 25 centimetres from the eye
11) The image formed on the retina is real and inverted. The retina comprises specialized cells that are sensitive to light, known as rod and cone cells. These cells get stimulated and send signals to the brain which turns them into erect images that allow us to see. So, the correct answer is 'real and inverted'.
12) The refraction of light caused by the earth's atmosphere (having air layers of varying optical densities) is called atmospheric refraction. If we look at objects through the hot air over a fire, the objects appear to be moving slightly.