Heat and Temperature — Physics STD 11 Science — Question

Read the passage given below and answer the following questions from 1 to 5. Satellites in a circular orbits around the earth in the equatorial plane with T = 24 hours are called Geostationary Satellites. Clearly, since the earth rotates with the same period, the satellite would appear fixed from any point on earth. It takes very powerful rockets to throw up a satellite to such large heights above the earth but this has been done in view of the several benefits of much practical application. Weight of an object is the force with which the earth attracts it. We are conscious of our own weight when we stand on a surface, since the surface exerts a force opposite to our weight to keep us at rest. The same principle holds good when we measure the weight of an object by a Spring balance hung from a fixed point e.g. the ceiling. The object would fall down unless it is subject to a force opposite to gravity. This is exactly what the spring exerts on the object. This is because the spring is pulled down a little by the gravitational pull of the object and in turn the spring exerts a force on the object vertically upwards. Now, imagine that the top end of the balance is no longer held fixed to the top ceiling of the room. Both ends of the spring as well as the object move with identical acceleration g. The spring is not stretched and does not exert any upward force on the object which is moving down with acceleration g due to gravity. The reading recorded in the spring balance is zero since the spring is not stretched at all. If the object were a human being, he or she will not feel his weight since there is no upward force on him. Thus, when an object is in free fall, it is weightless and this phenomenon is usually called the phenomenon of weightlessness. In a satellite around the earth, every part and parcel of the satellite has acceleration towards the centre of the earth which is exactly the value of earth’s acceleration due to gravity at that position. Thus in the satellite everything inside it is in a state of free fall. This is just as if we were falling towards the earth from a height. Thus, in a manned satellite, people inside experience no gravity. Gravity for us defines the vertical direction and thus for them there are no horizontal or vertical directions, all directions are the same.

1. Astronaut experiences weightlessness in space because:

1. Acceleration due to gravity is zero.
2. Actual weight of astronaut is zero.
3. They are going with same acceleration due to gravity.
4. None of these.

2. Weighing machine measures:

1. Mass of the person.
2. Normal reaction exerted by machine on person.
3. Both a and b.
4. None of these.

3. What is geostationary satellite?

4. What is weight? How it is measured?

5. What is weightlessness astronaut in satellite experienced by ?

The reduction factor K of a tangent galvanometer is written on the instrument. The manual says that the current is obtained by multiplying this factor to tane. The procedure works well at Bhuwaneshwar. Will the procedure work if the instrument is taken to Nepal? If there is some error, can it be corrected by correcting the manual or the instrument will have to be taken back to the factory?

Two stereo speakers are separated by a distance of 2.40m. A person stands at a distance of 3.20m directly in front of one of the speakers as shown in figure, Find the frequencies in the audible range (20-2000Hz) for which the listener will hear a minimum sound intensity. Speed of sound in air = 320m/s.

The needle of a dip circle shows an apparent dip of 45° in a particular position and 53° when the circle is rotated through 90°. Find the true dip.

Read the passage given below and answer the following questions from (i) to (iv). Zeroth Law of Thermodynamics states that two systems in thermal equilibrium with a third system separately are in thermal equilibrium with each other. The Zeroth Law clearly suggests that when two systems A and B, are in thermal equilibrium, there must be a physical quantity that has the same value for both. This thermodynamic variable whose value is equal for two systems in thermal equilibrium is called temperature (T). Thus, if A and B are separately in equilibrium with C, TA = TC and TB = TC. This implies that TA = TB i.e. the systems A and B are also in thermal equilibrium. Zeroth Law of Thermodynamics leads to the concept of internal energy of a system. We know that every bulk system consists of a large number of molecules. Internal energy is simply the sum of the kinetic energies and potential energies of these molecules. A certain amount of heat is supplied to the system’ or ‘a certain amount of work was done by the system its energy changes.

1. Three thermodynamic systems are at temperature of 500 c .what can we say about them?

1. Heat flows between them
2. It obeys Zeroth Law of Thermodynamics
3. Temperature of one system will increase and temperature of remaining two will decrease
4. None of these

2. Zeroth law of thermodynamics helped in the creation of which scale?

1. Temperature
2. Heat energy
3. Pressure
4. Internal energy

3. State Zeroth Law of Thermodynamics:
4. Define Internal energy of system:

A lady cannot see objects closer than 40cm from the left eye and closer than 100cm from the right eye. While on a mountaineering trip, she is lost from her team. She tries to make an astronomical telscope from her reading glasses to look for her teammates.

1. Which glass should she use as the eyepiece?
2. What magnification can she get with relaxed eye?

A narrow pencil of parallel light is incident normally on a solid transparent sphere of radius r. What should be the refractive index if the pencil is to he focused.

1. At the surface of the sphere.
2. At the centre of the sphere.