Q: Do the atom of an element and its ion have same size?
A: No. The positive ion is smaller in size than the atom.
1. The negative ion is larger in size than the atom.
Q: Do you observe yellow light in street lamps? How is this produced?
A: Sodium vapours produce yellow light in street lamps.
Q: How many elliptical orbits are added by Sommerfeld in the thirds Bohr’s orbit? What was the purpose of adding these elliptical orbits?
A: Sommerfeld added two elliptical orbits to Bohr’s third orbit.
1. The purpose of adding these is to account for the splitting of line spectra which Bohr’s model failed to explain.
Q: Why is the sky blue?
A: The sky is blue because the molecules of N2 and O2 act as scattering centres in the sky for scattering of blue light.
1. The sizes of these molecules are comparable to the wavelength of blue light. So these scatter blue light.
Q: Suppose you are inside the water in a swimmingpool near an edge. A friend is standing on the edge. Did you find your friend taller or
shorter than his usual height.
A: The friend seems to be taller than his actual height.
1. This is because the light ray travels from a rarer medium (air) to denser medium gets refraction and bends towards the normal.
2. This seems to be coming from a distant point for the swimmer. So the person appears taller than his usual height.
Q: In what cases does a light ray not deviate at the interface of the two media?
A: The light ray which incidents along the normal to the interface does not deviate at the interface of the two media.
Q: How do you identify the denser medium is the given two media?
A: Denser medium is the medium which has more refractive index and rarer medium has less refractive index in the given two media.
Q: Why does transfer of heat energy take place between objects?
A: When two objects are placed in thermal contact, heat energy will be transferred from ‘hotter body’ to the ‘cooler body’.
1. Transfer of heat energy take place between two objects due to the temperature difference in the objects.
Q: How is the temperature related to the kinetic energy of the molecules of a body?
A: Temperature of a body is an indicator of the average kinetic energy of molecules of that body.
1. The average kinetic energy of the molecules is directly proportional to the absolute temperature.
Q: Mention the uses of Propane, giving its formula.
A: Propane is a colourless and odourless gas often used as a heating and cooking fuel. Its chemical formula is C3H8.
Q: Why does the power supply fail to our home, sometimes during rainy season?
A: Sometimes during rainy season the power supply to our home from the electric pole will be interrupted due to the formation of
metal oxide layer on the electric wire.
1. This metal oxide is an electric insulator.
2. On removing the metal oxide layer formed on the wire with a sand paper, supply of electricity can be restored.
Q: Name the mirror in which the magnification is always less than one.
A: The magnification is always less than one in a convex mirror.
Q: The magnification produced by a plane mirror is +1. What does this mean?
A: 1. As the magnification is +1, it means the height of the image is the same as the height of the object.
2. It also implies that the object distance from the plane mirror is equal to the image distance from the plane mirror.
Q. Mention few natural acid-base indicators.
A: There are many natural materials like litmus, extract of red cabbage, turmeric solution and extracts of some flowers contain dye molecules which are weak acids or bases.
1. These can be used as acid-base indicators to detect the nature of the solution for acidity or basicity.
2. These are natural acid-base indicators.
Q. Are plants and animals pH sensitive? Explain.
A: Living organism can survive only in a narrow range of pH change. When pH of rain water is less than 5.6, it is called acid rain.
1. When acid rain flows into the rivers, it lowers the pH of river water, the survival of adequate life in such rivers becomes difficult.
Practice Questions:
1. What is nl x method? How is it useful?
2. Q: What is the focal length of a double concave lens kept in air with two spherical surfaces of radii, R1 = 30 cm and R2 = 60 cm? Take refractive index of lens as n = 1.5.
3. What do you mean by power of a lens?
4. Q: What mass of water at 100° C must be heated so as to form steam at 100° C when a burner supplies 10,800 calories of heat energy?