Q: How does eye lens change its focal length?
A: The ciliary muscle to which eye lens is attached helps the eye lens to change its focal length by changing the radii of curvature
of the eye lens.
Q: What can we do to correct myopia?
A: To correct myopia, we use a concave lens.
Q: Is the speed of light of each colour different?
A: Speed of light for all colours is the same in vacuum.
1. Speed of light for each colour is different in a medium.
Q: When do you see a rainbow in the sky?
A: On a rainy day we can see a rainbow in the sky.
1. The beautiful colours of rainbow are due to dispersion of sun light by millions of tiny water droplets.
Q: What is angle of vision? What is its value?
A: The maximum angle, at which we are able to see the whole object is called angle of vision.
1. The angle of vision for a healthy human being is about 60°. It varies from person to personand with age.
Q: Define intensity of light.
A: The intensity of light is the energy of light passing through unit area of plane, taken normal to the direction of propagation of light in one second.
Q: How does a rainbow appear for an observer in an aeroplane flying high?
A: An observer in an aeroplane observes the rainbow as a complete circle.
1. A rainbow is a three dimensional cone of dispersed white light of the sun and it appearsas a circle which is the base of the cone.
Q: Can a virtual image be photographed by a camera?
A: We can photograph the image formed in a plane mirror, which is a virtual image.
1. So it is possible to photograph a virtual image. Just as our eye can see the virtual image.
2. The camera can also record the virtual image.
Q: How do rays bend when they are incident on a curved surface?
A: A ray bends towards the normal when it travels from a rarer medium to a denser medium.
1. A ray bends away from the normal when it travels from a denser medium to a rarer medium.
Q: Can you get an image on the screen for every object distance?
A: We get an image of an object on the screen when it is placed at the focus and beyond it from a convex lens.
1. We do not get the image of an object on the screen, when the object is placed in between the optic centre and focus of the convex lens.
Q: Can you find the minimum limiting object distance for obtaining a real image? What do you call this minimum limiting object distance
for real image.
A: To get the real image (image on the screen) the object should be atleast placed at the focus or beyond the focus of the convex lens.
1. This minimum limiting object distance for real image is called the focal length of the convex lens.
Q: Why do all materials not act as conductors?
A: Only some materials act as conductors because they possess a large number of free electrons.
Q: Can you guess the reason why the ratio of V and I in case of LED is not constant?
A: LED is a non-ohmic material. So the ratio of V and I in the case of LED is not constant.
Q: Why does overload cause damage to electric appliances?
A: Due to overload, the heat increases in the circuit and this melts the parts in the electric appliances included in the circuit.
1. This overload causes damage to the electrical appliances.
Q: What do you mean by equivalent resistance?
A: If the current drawn by a resistor is equal to the current drawn by the combination of resistors then the resistor is called equivalent
resistor, provided the source in the circuit is constant.
Q. How do carbon atoms form bonds in so many different ways?
A. As per valence bond theory, the four unpaired electrons in a carbon atom is the main cause to form many bonds.
Q. Do you know what is a catalyst?
A. A catalyst is a substance which regulates (increase / decrease) the rate of a given reaction without itself finally undergoing any chemical change.
Q. Can we calculate the force experienced by a charge moving in a magnetic field.
A. We can calculate the force experienced by a charge moving in a magnetic field.
1. If F is that force, then F = qVB where q is the charge, B is magnetic induction and V is the velocity with which the charge is moving.
1 Mark Practice Questions:
1. Find the radii of curvature of a convexoconcave convergent lens made of glass with refractive index 1.5, having focal length of 24 cm. One of the radii of curvature is double the other.
2. The speed of light in a diamond is 1,24,000 km/s. Find the refractive index of diamond if the speed of light in air is 3,00,000 km/s
3. Why is it difficult to shoot a fish swimming in water?
4. Represent carbon dioxide molecule using Lewis notation.
5. Why do atoms of elements try to combine and form molecules?
6. What is bond angle in a molecule?
7. What do you understand when we say ‘Like dissolves in like’?
8. How does the valency vary on going down a group?
9. In Na, Al pair which is larger is size?
10. What do you understand by the term ‘First loinization energy’?
11. Explain the term ‘Halogen family’.
12. What is the speed of an electromagnetic wave?
13. Write the four quantum numbers for the differentiating election of sodium atom.