Three identical bar magnets are rivetted together at centre in same plane as shown in figure. This system is placed at rest in a slowly varying magnetic field. It shows that system of magnets does not show any motion. The N-S poles of one magnet is shown in the figure. Determine the poles of remaining two. |
If the base region of a transistor is made large, as compared to a usual-transistor, how does it affect |
(i) the collector current and |
(ii) current gain of this transistor? |
Early people thought that the God's was responsible for thunderbolts and that lightning stones, the super heads of lightning bolts, could be found buried, where lightning had struck. These stones were believed to give protection from illness and evil. But now we understand that cloud polarisation induces a charge on the Earth's surface. When the electric field becomes large enough, an electric discharge results, which we call car lightning. |
(i) What values do we learn from above discussion? |
(ii) An old saying suggests that it is safer to run faster than walk during an overhead lightning storm, and it has been observed that catties are more likely to be killed by a nearby lightning strike than humans. Comment. |
Complete the following block diagram depicting the essential components (or elements) of a basic communication system: |
Name the two basic modes of communication. Which of these modes is used for telephonic communication? |
Give reason. |
(i) Lighter elements are better moderators for a nuclear reactor than heavier elements. |
(ii) In a natural uranium reactor, heavy water is preferred moderator over ordinary water. |
Or |
How does the size of a nucleus depend on its mass number? Hence, explain why the density of nuclear matter of independent of the size of nucleus? |
Two signals A and B as given below, are applied as input to (i) NOR and (ii) NAND gates. Draw the output waveform in each case. |
Seeta did comb on her dry hair and after combing her hair she realised that the power of attracting small bit of paper has developed in comb but her sister Geeta did the same with oily hair and realised the comb could not attract small bits of paper this time. Now Geeta overviewd the complete situation and asked her teacher the reason behind this. |
Read the above passage and answer the following questions. |
(i) What according to you are the values displayed by Seeta? |
(ii) Explain the phenomenon involved. |
A 200 V variable frequency AC source is connected to a series combination of L = 5 H, \[C=80\mu F\text{ }\]and \[R=40\,\Omega .\] Calculate |
(i) angular frequency of source to get the maximum current in the circuit |
(ii) current amplitude at resonance |
(iii) power dissipation in the circuit |
(i) percentage modulation |
(ii) components of modulated wave |
(iii) the amplitude of each sideband. |
In a plane EM wave, the electric field oscillates sinusoidally at a frequency of \[2.0\times {{10}^{10}}Hz\] and amplitude \[48\,V{{m}^{-1}}.\] |
(i) What is the wavelength of a wave? |
(ii) What is the amplitude of the oscillating magnetic field? |
(iii) Show that the average density of E field equals to the average energy density of the B field. |
Rajveer switched On his radio set to listen his favourite music. But he found that the reception was not clear. Apart from that, there was overlapping of signals. Then, he had to adjust the tuner in the set to hear crisp and clear music. |
(i) Name the components of the tuner in the radio set. Also, write the component that was changed to adjust the tunes. |
(ii) Give reason, why the tuner was adjusted. |
(iii) Write the value that can be associated with the phenomenon involved in the adjustment of the tuner. |
In the given diagram, a piece of pure Semiconductor S in series with a variable resistor R and source of constant voltage V. Would you increase or decrease the value of R to keep the reading of ammeter A constant, when semiconductor S is heated? Give reason. If semiconductor is replaced by metal and it is heated then how the value of R should be changed to keep reading of ammeter A unchanged? |
(i) A convex lens is placed on an optical bench and is moved till it gives a real image of an object at minimum distance of 80 cm from the latter. Find the focal length of the lens. If object is placed at a distance of 15 cm from the lens, find the position of image. |
(ii) A double convex lens is made of glass of refractive index 1.5 with both faces of the same radius of curvature. |
Find the radius of curvature required, if the focal length is 15 cm. |
(i) What is the magnitude of current induced in the loop? |
(ii) Will there be any work done by the loop? Give reason for your answer. |
(iii) If the magnetic flux linked with the loop is given by \[{{\phi }_{m}}=6{{t}^{3}}-4{{t}^{2}}+2t+20,\] then calculate the induced emf in the coil at t = 4s |
Careful measurement of the electric field at the surface of a black box indicates that the net outward flux through the surface of box is \[8\times {{10}^{3}}N{{m}^{2}}{{C}^{-1}}.\] |
(i) What is the net charge inside the box? |
(ii) If the net outward flux through the surface of the box was zero, what can you conclude about the presence of charges inside the box. |
Draw a labelled ray diagram of an astronomical telescope, forming the image at infinity. |
An astronomical telescope uses two lenses of powers 10D and 1D. |
(i) State with reason, which lens is preferred of objective and eyepiece. |
(ii) Calculate the magnifying power of the telescope, if the final image is formed at the near point. |
Define the Q value of a nuclear process. When can a nuclear process not proceed spontaneously? |
If both the number of protons and the number of neutrons are conserved in a nuclear reaction, in what way is mass converted into energy (or vice-versa) in a nuclear relation? |
Or |
Using Bohr's postulates, derive the expression for the frequency of radiation emitted when electron is hydrogen atom undergoes transition from higher energy state (quantum number \[{{n}_{i}}\]) to the lower state \[({{n}_{f}}).\] |
When electron in hydrogen atom jumps from energy state \[{{n}_{i}}=4\] to \[{{n}_{f}}=3,\] identify the spectral series to which the emission lines belong. |
Pragiti's father was riding a scooter on highway and she was sitting behind him. While sitting, she observed that at a place when traffic signal turned red from green, her father still continued riding without noticing the signal change. |
Pragiti observed the whole situation and said her father to stop. Her father felt happy on his daughter's intelligence. |
Read the above passage and answer the following questions: |
(i) Which principle is used in maintaining the traffic signals? |
(ii) Write an expression for the speed of the photoelectrons. |
(iii) Why Pragiti's father became happy? |
What kind of values are expressed by Pragiti? |
(i) What do you mean by current sensitivity of a moving coil galvanometer. On what factor does it depend? |
(ii) State two reasons why a galvanometer cannot be used as such to measure high order current in a given circuit? |
(iii) The current sensitivity of a moving coil galvanometer is 5 div/mA and voltage sensitivity is 20 div/volt. Find the resistance of the galvanometer. |
Or |
(i) Write any three characteristics, a ferromagnetic substance should possess, if it is to be used to make a permanent magnet. Give one example of such a material. |
(ii) The susceptibility of a magnetic material is - 0.085. Identify the magnetic type of the material. |
(iii) A Rowland ring of mean radius 15 cm has 3500 turns of wire wound on a ferromagnetic core of relative permeability 800. What is the magnet field (B) in the core for a magnetising current of 1.2 A? |
A ray of light goes from medium 1 to medium 2, velocity of light in the two mediums are \[{{C}_{1}}\] and \[{{C}_{2}},\] respectively. For an angle of incidence, \[\theta \] in medium 1. The corresponding angle of refraction in medium 2 is \[\theta /2.\] |
(i) Which of the two media is optically denser and why? |
(ii) Establish the relationship among \[\theta ,\] \[{{c}_{1}}\] and \[{{c}_{2}}.\] |
(iii) The critical angle of incidence in a glass slab placed in air \[45{}^\circ .\] What will be the critical angle when it is immersed in water of refractive index 1.33? |
Or |
A beam of light of wavelength 400 nm is incident normally on a right angled prism as shown in the figure at night. |
It is observed that the light just grazes along the surface AC after falling on it. |
Given that the refractive index of the material of the prism varies with the wavelength \[\lambda \] as per the relation, |
(i) The following graph shows the variation of terminal potential difference V, across a combination of three cells in series to a resistor versus current I. |
Graph of terminal potential difference |
(a) Calculate the emf of each cell. |
(b) For what current I, will the power dissipation of the circuit be maximum? |
(ii) Determine the current drawn from a 12 V supply with internal resistance \[0.5\,\Omega \] by the infinite network shown in given figure. Each resistor has \[1\,\Omega \] resistance. |
OR |
(i) Derive an expression for drift velocity of free electrons in a conductor in terms of relaxation time. |
(ii) At room temperature \[(27{}^\circ C),\] the resistance of a heating element in \[100\,\Omega .\] What is the temperature of the element if the resistance is found to be \[117\,\Omega ,\] given that the temperature coefficient of resistance of the material of the resistor is \[1.70\times {{10}^{-4}}/{}^{o}C.\] |
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