Ques.71. The eccentricity of a hyperbola is equal to
Less than once
Greater than one
One
There is no term as eccentricity for a parabola
Answer.2. Greater than one
Explanation:-
The eccentricity of a hyperbola can be any real number greater than 1.
Ques.72. The angle between the vertical iso-axis and the rest of the two iso-axis are:-
15° each
90° each
30° each
60° each
Answer.3. 30° each
Explanation:-
The angle between the vertical iso-axis and the rest of the two iso-axis is 30° each
Ques.74. The acceleration due to gravity g is
Independent of the mass of the earth
Inversely proportional to the radius of the earth
Proportional to the mass of the earth and inversely proportional to the square of the radius of the earth
Same as the Poles and the equator
Answer.3. Proportional to the mass of the earth and inversely proportional to the square of the radius of the earth
Explanation:-
The acceleration due to gravity for all objects at the earth’s surface is proportional to the mass of the earth and inversely proportional to the square of earth radius at that point. The constant of proportionality is G
g = GM/r2
Ques.75. Rohan (mass 40 kg) and Sohan (mass 60 kg) climb the stairs of their school building to reach the first floor in the 40s and 60s, respectively. Let P1 and P2 be the power delivered in this task by Rohan and Sohan respectively. Which one of the following is correct?
P1 = P2
P1 > P2
P1 < P2
P1 = 2P2
Answer.4. P1 = P2
Explanation:-
Given
Rohan mass M1 = 40 kg
Sohan Mass M2 = 60
Time taken by Rohan T1 = 40s
Time taken by Sohan T2 = 60s
Since both have to reach the first floor, therefore, height is same
Work = mgh
W1 = M1gh = 40 J
W2 = M2gh = 60 J
Power = Work/time
P1 = W1/T1 = 40/40 = 1 J/S
P2 = W2/T2 = 60/60 = 1J/S
Therefore P1 = P2
Ques.76. The loudness or softness of a sound is determined basically by its
Amplitude
Frequency
Speed
Speed and frequency both
Answer.1. Amplitude
Explanation:-
The loudness or softness of a sound is determined basically by its amplitude. The amplitude of the sound wave depends upon the force with which an object is made to vibrate.
Ques.77. A ray of light traveling in air is incident on a glass slab, Part if it is reflected and part is refracted. Let i, r and s be the angle of incidence, an angle of reflection and angle of refraction. Which one of the following is correct?
i = r = s
i ≠ r ≠ s
i = r and s < i
i = r and s > i
Answer.3. i = r and s < i
Explanation:-
A transparent substance in which light travels is known as a medium. Air, glass, certain plastics, water, kerosene, alcohol, etc., are all examples of the medium. A medium in which the speed of light is more is known as an optically rarer medium (or less dense medium). Air is an optically rarer medium as compared to glass and water. A medium in which the speed of light is less is known as an optically denser medium.
When a ray of light goes from a rarer medium to a denser medium, it bends towards the normal tat point of incidence). In this case, the angle of refraction is smaller than the angle of incidence i.e s < i
According to the second law of reflection: The angle of reflection is always equal to the angle incidence. If the angle of incidence is i and the angle of reflection is r then:
i = r
Hence when a ray of light traveling in air is incident on a glass slab then the angle of incidence is equal to the angle of reflection but it is greater than the angle of refraction
i.e i = r and s < i
Ques.78. A conducting wire has length l and area of cross-section A. The resistivity of its material is ρ and its wire resistance is R. It is connected in series with another wire of the same dimensions but of a resistivity 2ρ. The net resistance of the combination is
R
2R
3R
2R/3
Answer.3. 3R
Explanation:-
Since the resistivity R is proportional to the resistivity ρ
R = ρL/A
Since all the dimensions are the same
R = ρ
So the resistance of the second wire will become 2R
Resistance in series = R + 2R = 3R
Ques.79. Which one of the following changes will decrease the vapor pressure of water contained in a sealed tube?
Increasing the quantity of water
Decreasing the quantity of water
Decreasing the temperature of the water
Decreasing the volume of the vessel
Answer.3. Decreasing the temperature of the water
Explanation:-
Vapour pressure
When a liquid is placed in a closed container such as a bottle with a stopper, the space above the liquid fills up with vapor. Liquid molecules evaporate into space above the liquid, whether it contains air or not.
The vapor molecules collide with the walls of the container, bounce off, and cause pressure. This pressure, called the vapor pressure, is added to the air pressure already present (due to the air molecules). The maximum vapor pressure that can be developed by a liquid is called the saturated vapor pressure of that liquid. Since the fraction of molecules with high energy increases with temperature, evaporation increases as the temperature rises, and the saturated vapor pressure increase with temperature. The magnitude of the saturated vapor pressure depends on the identity of the liquid and the temperature; it does not depend on the amount of liquid present.
The vapor pressure is directly related to the temperature of the liquid, higher water temperatures produce higher vapor pressures. Hence to decrease the vapor pressure we must decrease the temperature of the water.
Ques.80.Which of the following reaction represent the process of calcination?
Cu2S + O2 → Cu2O + SO2
CaCO3(s) → CaO(s) + CO2
ZnO(s) + C(s) → Zn(s) + CO(g)
2ZnS + 3O2 → 2ZnO + 2SO2(g)
Answer.2. CaCO3(s) → CaO(s) + CO2
Explanation:-
Calcining takes place in absence of air or oxygen to bring about a thermal decomposition. The calcining process normally takes place at temperatures above the thermal decomposition temperature but below the melting point of the product materials. The decomposition temperature is usually defined as the temperature at which the standard Gibbs free energy for a reaction is equal to zero.
For example, in limestone calcination, CaO is produced by the decomposition of lime (CaCO3) when CO2 is driven off on heating. This process is called calcination of lime and is an exothermic reaction.
