General Science MCQs by Aamir Mahar

Question 1: Which phenomena of light makes a pool of water appears to be less deep than it actually is?

(A) Refraction

(B) Reflection

(C) Diffraction

(D) Lateral inversion

Correct Answer: Option A

The rays of light coming from the bottom of the swimming pool travel from water to air. As the rays pass from denser medium (water) to rarer medium (air), they bend away from the normal. When the rays are produced back, they form an image of the bottom of the pool at a point above the real position. Therefore, the swimming pool appears to be less deep that it actually is. This phenomenon takes place due to the refraction of light at the interface of the two media.

Question 2: Stars appear to move from east to west because

(A) All stars move from east to west

(B) The earth rotates from west to east

(C) The earth rotates from east to west

(D) The background of the stars moves from west to east

Correct Answer: Option B

The motion of objects as perceived by an observer depends upon the frame of reference that the observer is present in with respect to the object. For example, a person sitting in a car sees the trees seemingly travelling backward. The truth is that the trees actually do not move but since the observer is in the car, his frame of reference with respect to the trees is moving forward along with the car. A similar thing happens when a person on the earth observes stars in the sky. The earth rotates from west to east and hence, in this frame of reference, the stars seem to travel in the opposite direction, that is, from east to west with respect to the observer. Therefore, stars seem to travel from east to west. Also note that the same explanation is valid as to why the sun rises in the east and sets in the west. The earth rotates from west to east and to us observers on the earth, it seems like the sun is in fact, travelling from the east (that is, rising in the east) to the west (that is setting in the west). An interesting fact is that for a person on Venus, the sun rises in the west and sets in the east. This is because Venus rotates from east to west.

Question 3:  Convex lenses are used for the correction of

(A) Hypermetropia

(B) Myopia

(C) Cataract

(D) Glaucoma

Correct Answer: Option A

When the light behind the retina is concentrated, hypermetropia occurs. The lens, therefore, adjusts its thickness, which helps to concentrate the light on the retina – a mechanism called accommodation. However, people with long sight are unable to completely cope, because the light does not focus sharply and vision is blurred. That is because the cornea is too thin, because the cornea is too low, or because the lens cannot be round enough. With glasses, the easiest, cheapest, and most reliable way to correct long-sightedness. Hypermetropia is when the eye is shorter than the average case, and if the target object is closer, the vision focuses behind the retina. This means that even when it hits the retina, it does not focus. Myopia is the condition when the eye is too long than the usual condition and when the target object is far away, the image falls short of the retina. In simpler terms, if the eye has myopia, then the eye will become too long and the image will fall short of the retina. And the eye is shorter in hypermetropia than in the normal case and the image is centered behind the retina. Hence a concave lens is suggested. A cataract is an opacification of the eye’s lens that leads to a loss of vision. Cataracts often grow slowly and one or both eyes may be affected. The solution is usually surgery. Glaucoma is a category of eye disorders that affect the optic nerve, the well-being of which is essential for good vision. This damage is also caused by pressure in your eye that is abnormally high. For people above the age of 60, glaucoma is one of the main causes of blindness. Also note that in microscopes and magnifying glasses, a convex lens is used to combine all incoming light rays to a single point. In cameras, a convex lens is used. For hyperopia correction, a convex lens is used. The converging lens is often used in the projector.

Question 4: Why are red coloured lights used in traffic signals to stop the vehicles?

(A) Minimum wavelength and less scatter.

(B) Maximum wavelength and more scatter.

(C) Maximum wavelength and less scatter.

(D) Less wavelength and less scatter.

Correct Answer: Option C

For stopping the vehicles moving on the rod, we use the light as a traffic signal. And this light must be in the visible region of the EM spectrum so that it can be perceived by the human eye. We know that the colours of lights which fall in the visible region are; violet, blue, green, yellow, orange, and red. The range of the wavelengths corresponding to the visible region is from 400nm of violet light to 700nm of red light. So we see that the wavelength of the violet light is the least and that of the red light is the maximum in the visible region. Now, in the path from the traffic light to the observer’s eye, lies the atmospheric particles. The atmospheric particles scatter the light which travels through them. This reduces the visibility of the signal. So we have to select the light which is least scattered by the atmospheric particles. As the wavelength of red light is maximum, so it is least scattered by the atmospheric particles. Therefore it is used in traffic signals. Also note that the scattering of light is responsible for many interesting phenomena occurring in nature. For instance, the sky appears blue because the blue light has a low wavelength and hence is more scattered by the atmospheric particles.

Question 5: Pencil lead is made up of which material?

(A) Graphite

(B) Charcoal

(C) Lead oxide

(D) Lampblack

Correct Answer: Option A

As we know that pencil is used for drawing and writing purposes. The pencil consists of a solid core inside a protective casing. The casing prevents the core from being broken down. The core is made up of an allotrope of carbon. We know that carbon has three allotropes: diamond, graphite and fullerene. The core of the lead pencil is made up of a mixture of graphite powder and clay. The lead pencil is actually a graphite pencil. The graphite pencil leaves behind a black or grey marks when written with it. The black or grey marks can be erased easily using an eraser. The black or grey marks are resistant to chemicals, moisture and natural aging. The core of lead pencil is made up of thin graphite which is enclosed in a shell of some other material which is made up of wood, plastic or recycled paper. Thus, lead pencil is made up of graphite powder which is an allotrope of carbon and not of lead metal. In early years, lead pencil was made up of graphite powder only. But nowadays it is made up of a mixture of graphite powder and clay. The graphite pencils are used for drawing which give smooth strokes.

Question 6: A solar cell converts:

(A) Heat energy into electrical energy

(B) Solar energy into electrical energy

(C) Heat energy into light energy

(D) Solar energy into light energy

Correct Answer: Option B

Solar cell is also known as photovoltaic cell. The photovoltaic effect is a phenomenon in which the electric current or the voltage is generated when the cell is exposed to the solar light. The solar cell is made up of semiconductors like silicon. Each solar cell is composed of two types of semiconductors namely; p-type and n-type. Both the types of semiconductors are joined to create a p-n junction where an electrical field is generated as the electrons and holes move to the positive p-side and the negative n-side respectively. Due to this electric field, the negatively charged particles tend to move in one direction and the positively charged particles in another. We know that the light is composed of photons i.e. electromagnetic radiation or energy. The energy from the photon gets transferred to an electron of the semiconductor as the light of suitable wavelength gets incident on it. As a result it jumps to a higher energy level called conduction band. Since the electrons are in their excited state now, they are free to move through the semiconductor. Thus, this movement of electrons generates electric current in the cell. Thus, a solar cell converts solar energy directly into electrical energy. The solar cell converts the solar energy directly into electrical energy with the help of photovoltaic effect. Also note that the solar light when incident on the cell makes the electrons move to the excited state due to which they tend to move through the material and the electric current is therefore generated. The two types of semiconductors used in the solar cell are p-type and n-type.

Question 7: The image formed on retina of the human eye is

(A) Real and Inverted

(B) Upright and Real

(C) Virtual and Upright

(D) Enlarged and Real

Correct Answer: Option A

The lens of the human eye is convex that mainly focuses on the light rays that path through it to create an image. The lens which is also convex further focuses the light so that it will hit the retina at the back of the eyeball that forms the image. The human eye enables us to see:

  • Light Rays enter the eye through the cornea. It acts as the front covering of an eye or the shield of an eye to protect it from the entrance of foreign particles and the process of refraction begins in the cornea.

  • The cornea and lens of an eye together from the real image on the retina when light passes into the eye, it passes first from the cornea since it has a curved surface and acts as the convex, it begins to focus on the light rays.

  • The light then passes over the pupil and hits the lens of the eye.

  • The lens which is also convex further focuses the light so that it will hit the retina at the back of the eyeball that forms the image. The image that is formed on the retina is real and inverted. The retina comprises specialized cells that are sensitive to light also known as rod and cone cells.

  • Both the cells get stimulated and send signals to the brain which turns them into erect images that allow us to see.

  • Then the light Rays pass through the pupil, it controls the intensity of light entering the eye, and then the light Rays pass through the convex lens.

  • Then the refracted Rays pass through a dense substance This substance is like a gel and is present in the eyeball. And finally, the image on the retina of an eye is formed.

  • The retina acts as a screen used to capture images and then this image is converted into electrical signals that are sent to the brain. The images reflected from the convex lens are real.

  • Thus real images are formed under the retina of the human eye.

Question 8: The blue colour of the water in the sea is due to

(A) Refraction of the blue light by the impurities in sea water

(B) Reflection of blue sky by the sea water molecules

(C) Absorption of other colours except for the blue colour by water molecules

(D) Scattering of blue light by water molecules

Correct Answer: Option B

The actual colour of sea water is not blue, but it appears to be blue. The ocean is blue because water absorbs colours in the red part of the light spectrum. Like a filter, this leaves behind colours in the blue part of the light spectrum for us to see. The ocean may also take on green, red, or other hues as light bounces off floating sediments and particles in the water. Blue colour of water in the sea is due to scattering of light by water molecules. As blue has smaller wavelength, therefore scattering of blue is exceptionally large. We know, scattering probability is directly proportional to 14 , where λ is the wavelength. The water of the sea is not blue but because of Rayleigh scattering, Particles and dissolved substances, depending on their size and physical properties (including the type of molecular bonds), will scatter or absorb visible light at different wavelengths and actually change the colour of the water. Therefore, the blue colour of the water of the sea is due to scattering of blue light by solid particles. Rayleigh scattering is wavelength dependent with shorter wavelengths being more scattered.

Question 9: Rainbow is formed due to which of the following?

(A) Absorption of sunlight in minute water droplets

(B) Diffusion of sunlight through water droplets

(C) Ionization of water deposits

(D) Refraction and reflection of sunlight by water droplets

Correct Answer: Option D

Reflection is the bouncing of light when it falls on an obstacle. Refraction is the bending of light when it passes through one medium into another. Dispersion is the splitting of white light into its constituent colours. What makes that rainbow appear as seven beautiful colours? It is due to the dispersion of the white when the light enters a water droplet in the atmosphere. Dispersion is the splitting of the white light into its constituent colours. Even in prism, we can this phenomenon. Dispersion is due to the refraction of the white light, when it enters a different medium. Refraction is the bending of light when it passes from one medium to another medium. This bending of light depends on the wavelengths of the light in both the mediums. Since light is made of different colours of different wavelengths, the deviation of each colour is different and we can see the constituent colours of the light, after the refraction. Therefore, when light enters a water droplet, it is first dispersed due to refraction. Then the dispersed light comes out of the water droplet and enters our eye. Since, all the colours come at different angles; we can see the light as a rainbow of several colours. That is why on rainy days we see a rainbow only when there is bright sunlight. When light enters from one medium to the other, some of it is reflected back and rest is refracted. Even when the refracted light falls on the other surface of the water droplet some it is internally reflected. Hence, a rainbow is formed due to the refraction, dispersion and reflection of the sunlight that passes through the water droplets present in the atmosphere. When light passes from a denser medium to a rarer medium, there is no refraction and instead of that reflection takes place. This kind of reflection is called total internal reflection. Total internal reflection depends on the angle of incident. If the angle of incident is more than a certain angle called the critical angle, the light is reflected back into the same medium and not refracted out.

Question 10: The oil in the wick of a lamp rises up due to

(A) Pressure difference

(B) Low viscosity of oil

(C) Capillary action

(D) Gravitational force

Correct Answer: Option C

The oil in the wick of an oil lamp rises up due to capillary action. This effect is due to surface tension of liquids. The wick here acts as a capillary tube. Adhesion of liquid to the walls of a vessel will cause an upward force on the liquid at the edges and result in a meniscus which turns upward. The surface tension acts to hold the surface intact. Capillary action occurs when the adhesion to the walls is stronger than the cohesive forces between the liquid molecules.