Blog provides NCERT solutions, CBSE, NTSE, Olympiad study material, model test papers, important Questions and Answers asked in CBSE examinations. References to Educational Sites and resources.
Q1(CBSE 2011): What is coliform bacteria? What does its presence in water indicate?
Answer: Coliform is a group of bacteria which is found in human intestines. Its presence in water indicates contamination by disease-causing microbes. Its high presence in rivers and ponds elevates the risks of water borne diseases like gastroenteritis.
Q2(CBSE 2011): State two reasons of launching "Ganga Action Plan". Which bacteria was found in Ganga water indicating contamination?
Dispersion of Light
Which light bends the most? credits:wpclipart
(NCERT Chapter Q & A, Other Questions asked in CBSE Exam)
Q1(NCERT): What is meant by power of accommodation of the eye?
Answer: Power of accommodation is the ability of the eye lens to focus near and far objects clearly on the retina by adjusting its focal length. Power of accommodation of the eye is limited. It implies the focal length of the eye lens cannot be reduced beyond certain minimum limit.
Q2(CBSE 2011): A person cannot see the objects distinctly, when placed at a distance less than 50 cm. (a) Identify the defect of vision. (b) Give two reasons for this defect. (c) Calculate the power and nature of the lens he should be using to see clearly the object placed at a distance of 25 cm from his eyes. (d) Draw the ray diagrams for the defective and the corrected eye.
Answer: (a) Defect of vision = Hypermetropia or Long-sightedness
Q1: Fill in the blanks.
(a) Hydro power plants convert _________ energy of falling water into electricity.
(b) When wood is burnt in a limited supply of oxygen, ______ is left behind as residue.
(c) Gases like ______, _____, ______ and ______ are generated in a biogas plant.
(d) Biogas contains _____ % methane.
(e) To maintain the required speed of the turbine, wind speed should be higher than _____.
(f) To establish 1 MW generator, the wind energy farm needs about ___ hectares of land.
(g) Ocean Thermal Energy plants can operate if the temperature difference between the water at the surface and water at depths up to ______ km is _______ or more.
(h) ______ and _______ countries have number of power plants based on geothermal energy.
Q & A Q1: What type of charge does an ebonite rod acquire when it is rubbed with wool? What is the nature of the charge acquired by wool?
Answer: Ebonite rod has a negative charge and woollen cap has an equal amount of positive charge.
Note: Charging by friction always produces equal and opposite charges on the twobodies which are rubbed in intimate contact.
Q2: What is the charge on an electron (e)?
Answer: -1.6 x 10 -19 Coulombs (C)
Q3: Define Coulomb's law.
Answer: The magnitude of the force of attraction (or repulsion) between two point charges is
directly proportional to the quantity of charge present on each of them and inversely
proportional to the square of the distance separating them.
Let q1 and q2 be two like charges separated by a distance d, then the two charges will continue to repel each other with a force (F). Mathematically it is represented as:
Q4: What is the SI unit of charge? Is it a scalar or vector quantity? Answer: SI unit of charge is Coulomb (C). It is a scalar quantity.
Q1: When an object is placed at a distance of 60 cm from a convex mirror, the magnification produced is 1/2. Where should the object be placed to get a magnification of 1/3?
Answer:
Q2: When an object is kept at a distance of 60cm from a concave mirror, the magnification is 1/2. Where should the object be placed to get a magnification of 1/3?
Answer: (Hint: steps are the same as in the above question, except it is a concave mirror, m = -1/2. Compute f in the first case i.e. f = -20 cm and the compute u in case II i.e. u = 80 cm)
Q3(CBSE Board): A concave lens made of material of refractive index (n1) is kept in a medium of refractive index (n2). A parallel beam of light is incident on the lens. Complete the path of the rays of light emerging from a concave lens if:
Q1: Name a light sensitive part of the eye where image of an object is formed. Answer: Retina
Q2: Name the muscle responsible for bringing change in the focal length of the eye lens ? Answer: Ciliary Muscles
Q3: Name one defect of vision which cannot be corrected by any type of spectacle lenses ? Answer: Cataract
Q4: What is the nature of image formed on the retina of the eye ? Answer: Real and inverted image.
Q5: Name the transparent membrane through which light enters the eye. Answer: Cornea
Q6: What type of signals are generated & sent to the brain by light sensitive cells of retina? Answer: Elctro-chemical Nerve signals are generated by rods and cones (photo sensitive cells of retina) and are sent to brain by optic nerve.
Numerical Problem on Light Reflection and Refraction
(More numerical and questions at this page) Q1: How fast does the light travel in a glass of refractive index 1.5?
Answer: By Snell's law, refractive index (n) is the ratio of i.e.
Q2:When a bright object is placed 10 cm away from a concave mirror, its real image is formed at a distance 40cm from the mirror. What is the focal length of the mirror?
Answer:
Q3: If the angle of incidence of a ray of light falling on the glass surface is 30° and the angle of refraction is 19°. what is the refractive index of glass?
Ans: angle of incidence i = 30°
angle of refraction r = 19°
refractive index n = sin i/sin r = sin 30/sin 19
n = .5/.3256 = 1.535 ....(ans)
Q4: If a child crawls towards a mirror at a rate of 0.20 m/s, then at what speed will the child and her image come nearby to each other?
Ans: In 1 sec, the child moves towards the mirror by a distance of 0.20 meters. In the same second, her image also moves 0.20m closer.
Therefore, the child and her image comes closer to each other by 0.40m per second.
1. Light is a form of energy. Since energy cannot be seen, we see objects in light.
2. A ray of light is a straight line which represents the path of traveling light. A collection of light rays is called a beam of light.
3. Q: How do we see objects?
Ans: The visual ability of humans is the
result of the complex interaction of light, eyes and brain.
We are able to see because light from an object can move
through space and reach our eyes. Once light reaches our
eyes, signals are sent to our brain, and our brain deciphers
the information in order to detect the appearance, location
and movement of the objects we are sighting at.
4. Luminous
objects are objects that generate their own
light. e.g. firefly, the sun.
5. Illuminated
objects are objects that are capable of
reflecting light to our eyes. e.g. the moon
6. A ray of light that falls on a surface is called incident ray.
7. The light that is sent back by the reflecting surface is called reflection.
8. The ray that is sent back by the reflecting surface is called the reflected ray.
9. When light falls on a body, it may be absorbed, may be transmitted or light may come back to the same medium.
10. Laws of Reflection (watch the you tube video):
a. First law of reflection: The incident ray, the normal to the surface at the point of incidence and the reflected ray, all lie in the same plane.
b. Second law of reflection: The angle of incidence is equal to the angle of reflection.
