A radar is able to detect the reflected waves from an enemy aero plane, after a time interval of 0.02 milliseconds. If the velocity of the waves is 3 x 108m/s, calculate the distance of the plane from the radar.
Velocity = 30. X 108m/s
Time = 0.02 milliseconds = 0.02 x 10-3 seconds
Now, using the formula,
This is the required distance of the plane from the radar.
i) What is meant by refraction?
ii) Express the refractive index n of a medium,
i) Refraction is the phenomenon in which a ray of light bends from its path as it attempts to move from one medium into another.
ii) 1. n =
2. n =
iii) It means that the refractive index of both the medium is the same.
i) Mention two important precautions that should be taken while handling radioactive materials.
ii) State any one use of radioisotopes.
1. Storage of rad ioactive substance should be done with great care; they should be enclosed by lead blocks and further surrounded by concrete walls.
2. Artificial, long mechanical ‘arms’ should be used to handle the more dangerous sources.
ii) They are used to study the function of fertilizers for different plants. They have also been used for developing new species of a plant by causing genetic mutations.
i) State the function of a split ring in a D.C. motor.ii) Mention two reasons why a soft iron core is used within the coil of a moving coil galvanometer?
Split ring in a D.C. motor keeps the direction of current same in order to keep the direction of motion constant.
1. Soft iron core produces a very strong magnetic field. It intensifies the magnetic field.
2. It also helps in radial magnetic field.
A solid body weighs 2.10 N in air. Its relative density is 8.4. How much will the body weigh if placed:-
i) in water,ii) in a liquid of relative density 1.2?
Weight in air = 2.10 N
R.D = 8.4
i) RD =
Upthrust = =
Weight of the body in water = 2.10 – 0.25 = 1.85 N
Loss of weight in liquid = RD x loss of weight in water
= 1.2 x 0.25
= 1.85 N
Therefore, weight of the body in liquid = 2.1 – 0.3
= 1.8 N
i) A glass slab is placed over a page on which the word VIBGYOR is printed with each letter in its corresponding color.
1. Will the image of all the letters be in the same plane?
2. If not, state which letter will be raised to its maximum. Give a reason for your answer.ii) What will be the color of an object, which appears green in white light and black in red light?
1. No, the image of all letters will not be at the same place.
2. Letter V will be raised maximum. This is because the refractive index of a material depends inversely upon the wavelength of light. On the other hand the shift in the image depends directly on the refractive index. Since, the refractive index of a material is maximum fr violet light, therefore letter V which is written with violet colour is raised the maximum.
ii) Green will be the actual color of an object.
An electrical appliance is rated 1500 W, 250 V. This appliance is connected to 250 V mains.
i) The current drawn?
ii) The electrical energy consumed in 60 hoursThe cost of electrical energy consumed at Rs. 2.50 per kWh.
a) Power, P = 1500 W, Voltage, V = 250 V
i) I = ?
P = VI
I = ?
I = P/V = 1500 / 250 = 6 A
ii) Electrical energy consumed, E = Px t = 1500 x 60 = 90,000 Wh = 90 kWh
iii) Cost = 90 x 2.50 = 90 x = Rs. 225
A piece of ice is heated at a constant rate. The variation of temperature with heat input is shown in the graph alongside:-
i) What are represented by AB and CD?ii) What conclusion can you draw regarding the nature of ice from the alongside graph?
i) AB represents the time required by ice to change from ice at 0oC into water at 0o C.
CD represents the time required by water to change from water at 100oC into steam at 100oC.
ii) Ice is made of pure water, as its melting point and its boiling point are 0o C and 100oC respectively.
The combination of a movable pulley P1 with a fixed pulley P2 is used for lifting up a load W.
i) State the function of the fixed pulley P2.
ii) If the free end of the string moves through a distance C, find the distance by which the load W is raised.
iii) Calculate the force to be applied at C to just raise the load W = 20 kgf, neglecting the weight of the pulley P1and friction.
The fixed pulley P2 only changes the direction of the force. i.e., force can be applied downwards which is more convenient.
The load will be raised by a distance x/2
Distance moved by load dL= x/2
Distance moved by the effort, dE= x
Load (L) = 20 kgf
Effort = ?
Load x Load arm = effort x effort arm
State the functions of the following in a nuclear reactor:-i) Moderator ii) Control rods iii) Coolant
i) Moderator – It shows down the speed of moving neutrons to allow the nuclear fission of uranium.
ii) Control rods – They absorb the extra neurons which are released during the nuclear fission reaction. They absorb that much neurons so that only one neuron is left to carry out controlled nuclear fission. They are made of boron and cadmium.
iii) Coolant – It absorbs the heat released during nuclear fission reaction. It is used to carry the energy of the fission reaction from the core of the reactor and take it to a place of utilization in steam generator.