Why does the Sun appear reddish early in the morning?
In the early morning sun is at the farthest distance from the earth.
When the white light beam passed through the transparent glass tank having clear water, a converging lens is placed between them. After the glass tank a cardboard is placed having a circular hole in it, in which light ray passed on the screen by using another converging lens. Add 200g of sodium thiosulphate and 1- 2ml of concentrated sulphuric acid to 2L of clean water in the tank, then the sulphur particles begins to form in 2- 3 minutes. We can observe the light with the smaller wavelength, i.e, blue from the three sides of the glass tank will scatter and from the fourth side we will see the red light that pass into the circular hole, reaches to the human eyes.
As in the above paragraph mentioned, the sun colour appearance is described in the same way. The sun appears red in the early morning because when the light from the sun near the horizon passes through the atmospheric thick layers, blue light with shorter wavelength will scatter and the red light will reach to the eyes having longer wavelength.
What is the far point and near point of the human eye with normal vision?
Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is 1 m. What is the power of the lens required to correct this defect? Assume that the near point of the normal eye is 25 cm.
Why do stars twinkle?
Explain why the planets do not twinkle.
What is meant by power of accommodation of the eye?
The human eye forms the image of an object at its
(a) cornea. (b) iris. (c) pupil. (d) retina.
A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?
The least distance of distinct vision for a young adult with normal vision is about
(a) 25 m. (b) 2.5 cm. (c) 25 cm. (d) 2.5 m.
A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used to restore proper vision?
The change in focal length of an eye lens is caused by the action of the
(a) pupil. (b) retina.
(c) ciliary muscles. (d) iris.
Did Döbereiner’s triads also exist in the columns of Newlands’ Octaves? Compare and find out.
What is a good source of energy?
Why is diffusion insufficient to meet the oxygen requirements of multi-cellular organisms like humans?
What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
What changes can you make in your habits to become more environment-friendly?
What is the difference between a reflex action and walking?
What is the importance of DNA copying in reproduction?
If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
Why should a magnesium ribbon be cleared before burning in air?
Define the principal focus of a concave mirror.
What would be the advantages of exploiting resources with short-term aims?
How would these advantages differ from the advantages of using a long-term perspective in managing our resources?
What changes would you suggest in your home in order to be environment-friendly?
The essential difference between an AC generator and a DC generator is that
(a) AC generator has an electromagnet while a DC generator has permanent magnet.
(b) DC generator will generate a higher voltage.
(c) AC generator will generate a higher voltage.
(d) AC generator has slip rings while the DC generator has a commutator.
State whether the following statements are true or false.
(a) An electric motor converts mechanical energy into electrical energy.
(b) An electric generator works on the principle of electromagnetic induction.
(c) The field at the centre of a long circular coil carrying current will be parallel straight lines.
(d) A wire with a green insulation is usually the live wire of an electric supply.
Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field?
Why don’t two magnetic field lines intersect each other?
Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.)
(a) mass (b) speed
(c) velocity (d) momentum
A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (i) pushed into the coil, (ii) withdrawn from inside the coil, (iii) held stationary inside the coil?
What is the function of an earth wire? Why is it necessary to earth metallic appliances?