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Dilpreet 14/05/2016 in  IIT JEE Coaching classes

What is electronegativity?

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Educa Academy replied | 14/05/2016

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.

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Shivaji replied | 15/06/2016

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. The Pauling scale is the most commonly used. Fluorine (the most electronegative element) is assigned a value of 4.0, and values range down to caesium and francium which are the least electronegative at 0.7.

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Manjunath 14/05/2016 in  IIT JEE Coaching classes

What do the terms 'mesomeric effect' and 'inductance effect' mean?

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Chaitanya replied | 07/06/2016

Mesomeric effect" is just a synonym for "resonance effect". If electron density at a particular point in a molecule is higher or lower than what you'd expect from a single Lewis structure, and various canonical structures can be drawn to show how electron delocalization will explain the discrepancy, the difference in electron density is called a "mesomeric effect".
An inductive...  more»
Mesomeric effect" is just a synonym for "resonance effect". If electron density at a particular point in a molecule is higher or lower than what you'd expect from a single Lewis structure, and various canonical structures can be drawn to show how electron delocalization will explain the discrepancy, the difference in electron density is called a "mesomeric effect".
An inductive effect is the polarization of a chemical bond caused by the polarization of an adjacent bond. (Field effects are polarization caused by nonadjacent bonds). «less

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Alpine replied | 05/07/2016

mesomeric effect is seen in only conjugated and unsaturated compounds and its involves delocalisations of Pi electrons including lone pair eletrons whereas inductive effect is seen in both saturated and unsaturated compounds and it involves tranmission of sigma electrons through carbon chain. I.E and M.E are permanant effects.

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Advm 14/05/2016 in  IIT JEE Coaching classes

How do I draw a Lewis structure for sucrose?

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Oasis Gurgaon replied | 14/05/2016

Start with the skeleton structure of sucrose. You can't figure out the skeleton structure with just the molecular formula in hand, as you've discovered. At each angle in the stick model, there is a carbon atom. Each carbon atom is connected to exactly 4 other things in this structure (there are no multiple bonds). The oxygens each must have two lone pairs to have an octet, because...  more»
Start with the skeleton structure of sucrose. You can't figure out the skeleton structure with just the molecular formula in hand, as you've discovered. At each angle in the stick model, there is a carbon atom. Each carbon atom is connected to exactly 4 other things in this structure (there are no multiple bonds). The oxygens each must have two lone pairs to have an octet, because each has two single bonds. «less

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Shivaji replied | 15/06/2016

Draw a skeleton structure
Count total valence electrons.
Connect the structure
Place electrons on outside atoms
Place all remaining electrons on the central atom.

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Harshitha 14/05/2016 in  IIT JEE Coaching classes

What is the difference between valence, and number of valence electrons?

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Oasis Gurgaon replied | 14/05/2016

The combining capacity of an atom is called its valency. Actually it can be defined as the number of electrons that an atom may lose (or) gain during a chemical reaction (or) the number of electrons shared.
Ex: In water molecule H?O (H - O -- H)
Valency of Hydrogen is 1 (as it combines with Oxygen atom by one single bond) and valence electrons in Hydrogen = 1
...  more»
The combining capacity of an atom is called its valency. Actually it can be defined as the number of electrons that an atom may lose (or) gain during a chemical reaction (or) the number of electrons shared.
Ex: In water molecule H?O (H - O – H)
Valency of Hydrogen is ‘ 1 ‘ (as it combines with Oxygen atom by one single bond) and valence electrons in Hydrogen = 1
Valency of Oxygen is ‘2’ (as it combines with two Hydrogen atoms by two bonds), but valence electrons in oxygen = 6
The numbers of electrons in outermost shell (or) valency shell of an atom are called valency electrons.
Based on valency electrons the group number of an atom can be found.
Ex: Number of valence electrons in chlorine are 7 so it belongs to VIIA - group, but its valency is 1.

So, it is to be understood that some times valency is equal to valence electrons, but not all the time «less

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Shivaji replied | 15/06/2016

Valence electrons are the number of electrons in the outermost energy level of an atom.
Valency is the number of electrons an atom needs to gain or lose in order to have a full outermost energy level.

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Yashraj 13/05/2016 in  IIT JEE Coaching classes

Mention the important considerations required while fabricating a p-n junction diode to be used as a Light Emitting Diode (LED). What should be the order of band gap of an LED if it is required to emit light in the visible range?

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Quest Academy replied | 13/05/2016

1. The reverse breakdown voltages of LEDs are very low, typically around 5V. So care should be taken while fabricating a p-n junction diode so that the high reverse voltages do not appear across them.
2. There is very little resistance to limit the current in LED. Therefore, a resistor must be used in series with the LED to avoid any damage to it.
The semiconductor used...  more»
1. The reverse breakdown voltages of LEDs are very low, typically around 5V. So care should be taken while fabricating a p-n junction diode so that the high reverse voltages do not appear across them.
2. There is very little resistance to limit the current in LED. Therefore, a resistor must be used in series with the LED to avoid any damage to it.
The semiconductor used for fabrication of visible LEDs must at least have a band gap of 1.8 eV (spectral range of visible light is from about 0.4 ?m to 0.7 ?m, i.e., from about 3 eV to 1.8 eV). «less

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Chetana 13/05/2016 in  IIT JEE Coaching classes

Write three important factors which justify the need of modulating a message signal. Show diagrammatically how an amplitude modulate wave is obtained when a modulating signal is superimposed on a carrier wave.

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Quest Academy replied | 13/05/2016

Three important factors which justify the need of modulating a message signal:
1. Size of antenna or aerial: For communication within the effective length of the antennas, the transmitting frequencies should be high, so modulation is required.
2. Effective power which is radiated by antenna: Since the power radiated from a linear antenna is inversely proportional to the...  more»
Three important factors which justify the need of modulating a message signal:
1. Size of antenna or aerial: For communication within the effective length of the antennas, the transmitting frequencies should be high, so modulation is required.
2. Effective power which is radiated by antenna: Since the power radiated from a linear antenna is inversely proportional to the square of the transmitting wavelength. As high powers are needed for good transmission so, higher frequency is required which can be achieved by modulation.
3. The interference of signals from different transmitters: To avoid the interference of the signals there is need of high frequency which can be achieved by the modulation. «less

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Antesh Chirag replied | 13/05/2016

In order to obtain only low frequency signal (a) it will need antenna of very large length i.e. 5 kms (b) get significant attenuation since power radiated by antenna is inversely proportional to square of wave length (c) mixing up of transmitted signals emitted from different stations

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Priya 13/05/2016 in  IIT JEE Coaching classes

Using Bohr’s postulates, obtain the expression for the total energy of the electron in the stationary states of the hydrogen atom. Hence draw the energy level diagram showing how the line spectra corresponding to Balmer series occur due to transition between energy levels.

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Chaitanya replied | 07/06/2016

The answer to the query that you have posted can be found in the NCERT text book Part II.
Kindly refer to page number 424 and 425 for your answer.
Also, the energy level diagram can be found on page number 429.

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Birjesh Choudhary replied | 05/07/2016

I hope this would clarify your doubt.

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Aditi 13/05/2016 in  IIT JEE Coaching classes

Distinguish between myopia and hypermetropia.

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Ritul replied | 13/05/2016

Myopia is short sightedness( one can easily see nearby objects clearly & has problems in seeing objects which are far) whereas hypermetropia is long sightedness ( the eye cannot focus clearly on the objects at shorter distance).
Myopia happens usually because of deficiencies in the body or due to other external factors like over use light emitting devices, reading from very...  more»
Myopia is short sightedness( one can easily see nearby objects clearly & has problems in seeing objects which are far) whereas hypermetropia is long sightedness ( the eye cannot focus clearly on the objects at shorter distance).
Myopia happens usually because of deficiencies in the body or due to other external factors like over use light emitting devices, reading from very close range etc. Whereas hypermetropia is usually genetic in nature. «less

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Shivaji replied | 15/06/2016

Both Myopia (short-sightedness) and Hypermetropia (long-sightedness) are common eye conditions that mean light does not focus on the retina of the eye. Both conditions can be easily corrected using prescription glasses or contact lenses or in mild cases by laser eye surgery.

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Prabhu 13/05/2016 in  IIT JEE Coaching classes

Why are OH, NH, and FH bonds so polar?

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Dr.s replied | 13/05/2016

Because the ddifference of electonegetivity of O and H, N and H and F and H is very high, which cause the pulling of shared electron pair clouds towards most eelectronegative atom.

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Shivaji replied | 15/06/2016

Hydrogen atoms are very small (with an atomic radius of about 37 pm, they're smaller than any other atom but helium). So when a bonded electronegative atom pulls electrons away from the hydrogen atom, the positive charge that results is tightly concentrated. The small size of the hydrogen atom is one factor responsible for the unusual strength of the dipole-dipole interaction we...  more»
Hydrogen atoms are very small (with an atomic radius of about 37 pm, they're smaller than any other atom but helium). So when a bonded electronegative atom pulls electrons away from the hydrogen atom, the positive charge that results is tightly concentrated. The small size of the hydrogen atom is one factor responsible for the unusual strength of the dipole-dipole interaction we call "hydrogen bonding". «less

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Mukesh 12/05/2016 in  IIT JEE Coaching classes

Which of the following waves can be polarized (i) Heat waves (ii) Sound waves?

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U.k. replied | 13/05/2016

Heat waves can be polarized because heat waves are transverse waves whereas sound waves cannot be polarized because sound waves are longitudinal waves.

Transverse waves can oscillate in the direction perpendicular to the direction of its propagation but sound waves oscillate only along the direction of its propagation. So,sound waves cannot be polarized.

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Quest Academy replied | 13/05/2016

Heat waves can be polarized because heat waves are transverse waves whereas sound waves cannot be polarized because sound waves are longitudinal waves.

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Prasad 12/05/2016 in  IIT JEE Coaching classes

State Lenz’s Law. A metallic rod held horizontally along east-west direction, is allowed to fall under gravity. Will there be an emf induced at its ends? Justify your answer.

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Birjesh Choudhary replied | 05/07/2016

The vertical component of earth's magnetic field will be cut by the movement of the horizontal rod,so a motional emf will be generated across the ends of the rod.

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Amit replied | 08/07/2016

yes, Because earth horizontal magentic field is from south to north, and because of gain in vel due to fall there will be induced emf vBl (vel * horizontal earth magnetic field * lenght of rod)

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Poonam 12/05/2016 in  IIT JEE Coaching classes

A capacitor has been charged by a dc source. What are the magnitudes of conduction and displacement currents, when it is fully charged?

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Chaitanya replied | 07/06/2016

Electric flux through the plates of the capacitor is given by,
? = q/?0 .(1)
Value of q is constant when capacitor is fully charged.
Hence from (1), ? will also be constant.
Displacement current = ID = ?0 (d? / dt) = 0 (? ? is constant)
Conduction current = Ic = C (dV/dt) = 0 (? V is constant)
? Ic = ID = 0 when...  more»
Electric flux through the plates of the capacitor is given by,
? = q/?0 …………….(1)
Value of q is constant when capacitor is fully charged.
Hence from (1), ? will also be constant.
Displacement current = ID = ?0 (d? / dt) = 0 (? ? is constant)
Conduction current = Ic = C (dV/dt) = 0 (? V is constant)
? Ic = ID = 0 when the capacitor is fully charged. «less

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C

Chitra 12/05/2016 in  IIT JEE Coaching classes

The given graph shows the variation of photo-electric current (I) versus applied voltage (V) for two different photosensitive materials and for two different intensities of the incident radiation. Identify the pairs of curves that correspond to different materials but same intensity of incident radiation.

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Chaitanya replied | 07/06/2016

Curves 1 and 2 represent same materials while curves 3 and 4 represent different materials, since the value of stopping potential for the pair of curves (1 & 2) and (3 & 4) are same.
For the given frequency of the incident radiation the stopping potential is independent of its intensity.
So the pair of curves (1 & 3) and (2 & 4) correspond to different materials but same...  more»
Curves 1 and 2 represent same materials while curves 3 and 4 represent different materials, since the value of stopping potential for the pair of curves (1 & 2) and (3 & 4) are same.
For the given frequency of the incident radiation the stopping potential is independent of its intensity.
So the pair of curves (1 & 3) and (2 & 4) correspond to different materials but same intensity of incident radiation. «less

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N

Neelima 12/05/2016 in  IIT JEE Coaching classes

A convex lens of focal length 25 cm is placed coaxially in contact with a concave lens of focal length 20 cm. Determine the power of the combination. Will the system be converging or diverging in nature?

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Bikramjeet replied | 13/05/2016

power will be -1Dioptre..as P= 1/F..for convex lens it is + 25 cm and for concave it is -20cm,,...as power is in -ve, combination will be diverging

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Quest Academy replied | 13/05/2016

We have focal length of convex lens,
f1 = +25 cm or +0.25 m and the focal length of concave lens (f2) = -20 cm or -0.20 m
Equivalent focal length F= 1/f1 + 1/f2 = 1/0.25 + 1/-0.20 = -1/100
Therefore F= -100 cm
Power of convex lens P1 = 1/f1 = 1/0.25
Power of concave lens P2 = 1/f2 = 1/-0.20
Power of the combination P = P1 + P2 = 1/0.25 +1/-0.20 = -1D
The...  more»
We have focal length of convex lens,
f1 = +25 cm or +0.25 m and the focal length of concave lens (f2) = -20 cm or -0.20 m
Equivalent focal length F= 1/f1 + 1/f2 = 1/0.25 + 1/-0.20 = -1/100
Therefore F= -100 cm
Power of convex lens P1 = 1/f1 = 1/0.25
Power of concave lens P2 = 1/f2 = 1/-0.20
Power of the combination P = P1 + P2 = 1/0.25 +1/-0.20 = -1D
The focal length of the combination = ?1 m = ?100 cm.
As the focal length is in negative, the system will be diverging in nature. «less

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T

Thamaraikannan 11/05/2016 in  IIT JEE Coaching classes

What ate permanent magnets? Give one example

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Praveen Kumar Rao replied | 12/05/2016

An object made from a material that is magnetized and creates its own magnetic field.
Eg: Refrigerator magnet used to hold notes on a refrigerator door.

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Bikramjeet replied | 13/05/2016

as it clear from the name magnet which donot loss its magnetic properties in the absence of current or induced field,earth is good example

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Himanshu 11/05/2016 in  IIT JEE Coaching classes

What is the geometrical shape of equipotential surfaces due to a single isolated charge?

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Praveen Kumar Rao replied | 12/05/2016

sphere centered on the point charge

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Quest Academy replied | 13/05/2016

For an isolated charge the equipotential surfaces are co-centric spherical shells and the distance between the shells increases with the decrease in electric field.

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Vikna 11/05/2016 in  IIT JEE Coaching classes

Define mutual inductance and write its S.I. units.

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U.k. replied | 11/05/2016

units of mutual inductance is Henry

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U.k. replied | 11/05/2016

If two coils of wire are brought into close proximity with each other so the magnetic field from one links with the other then a voltage is generated in the second coil. This phenomenon is called mutual inductance: when voltage is applied in one coil it induces a voltage in another.

example : transformer

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U.k. 12/05/2016 in  IIT JEE Coaching classes

Which of the following waves can be polarized (i) Heat waves (ii) Sound waves? Give reason to support your answer.

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Shivaji replied | 08/06/2016

heat waves can be polarized because heat waves are transverse waves whereas sound waves cannot be polarized because sound waves are longitudinal waves
Transverse waves can be oscillate in the direction perpendicular to the direction of its propagation but longitudinal waves like sound waves oscillate only along the direction of its propagation , so longitudinal waves cannot be polarized

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U.k. 12/05/2016 in  IIT JEE Coaching classes

A capacitor has been charged by a dc source. What are the magnitude of conduction and displacement current, when it is fully charged?

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Chaitanya replied | 07/06/2016

Ans. Electric flux through plates of capacitor, ?E ? q .

? o

Here, q ? constant, the capacitor is fully charged.

? q ?
d ?

d?E ? ?
Displacement current , ID ??? ??? ? o ? ? 0
o dt o dt


Conduction current, I ? C dVdt

when...  more»
Ans. Electric flux through plates of capacitor, ?E ? q .

? o

Here, q ? constant, the capacitor is fully charged.

? q ?
d ?

d?E ? ?
Displacement current , ID ??? ??? ? o ? ? 0
o dt o dt


Conduction current, I ? C dVdt

when the capacitor becomes fully charged.

Transverse waves can oscillate in the direction perpendicular to the direction of its propagation but longitudinal waves like sound waves oscillate only along the direction of its propagation. So, longitudinal waves cannot be polarized «less

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U.k. 12/05/2016 in  IIT JEE Coaching classes

Write the relationship between angle of incidence “i”™, angle of prism “A”™ and angle of minimum deviations for a triangular prism.

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Chaitanya replied | 07/06/2016

i=A+delta m/2

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Birjesh Choudhary replied | 12/07/2016

Angle of deviation for a prism is,
D= i+e-A
For minimum deviation,i=e
Dmin = 2i-A

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U.k. 12/05/2016 in  IIT JEE Coaching classes

A capacitor has been charged by a dc source. What are the magnitude of conduction and displacement current, when it is fully charged?

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Chaitanya replied | 07/06/2016

Ans. Electric flux through plates of capacitor, ?E ? q .

? o

Here, q ? constant, the capacitor is fully charged.

? q ?
d ?

d?E ? ?
Displacement current , ID ??? ??? ? o ? ? 0
o dt o dt


Conduction current, I ? C dVdt

when...  more»
Ans. Electric flux through plates of capacitor, ?E ? q .

? o

Here, q ? constant, the capacitor is fully charged.

? q ?
d ?

d?E ? ?
Displacement current , ID ??? ??? ? o ? ? 0
o dt o dt


Conduction current, I ? C dVdt

when the capacitor becomes fully charged.

Transverse waves can oscillate in the direction perpendicular to the direction of its propagation but longitudinal waves like sound waves oscillate only along the direction of its propagation. So, longitudinal waves cannot be polarized «less

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U.k. 12/05/2016 in  IIT JEE Coaching classes

A metallic rod held horizontally along east-west direction, is allowed to fall under gravity. Will there be an emf induced at its ends? Justify your answer.

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Chaitanya replied | 07/06/2016

when a metalic rod is held horizantally along east-west direction,is allowed to fall under gravity i.e. it falls from north to south,the intensity of magnetic lines of earth's magnetic field changes through it i.e. the magnetic flux changes and hence the induced emf in it.

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U.k. 12/05/2016 in  IIT JEE Coaching classes

A convex lens of focal length 25 cm is placed coaxially in contact with a concave lens of focal length 20 cm. Determine the power of the combination. Will the system be converging or diverging in nature?

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Chaitanya replied | 07/06/2016

f1=0.25m,f2=-0.20m,F=(1/f1)+(1/f2)=-1m
since the focal length is negative,system will be diverging in nature.

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Birjesh Choudhary replied | 05/07/2016

Total power is the sum of the powers of lenses in contact.
P=P1+P2
focal length=1/(Power of lens)
Total Power= 1/.25 + 1/(-.2) =-1D
Since, power is negative, the system will act a diverging lens.

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Name 10/05/2016 in  IIT JEE Coaching classes

In a double slit experiment using light of wavelength 600 nm, the angular width of the fringe formed on a distant screen is 0.1°. Find the spacing between the two slits.

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Dr K Venkateswarlu replied | 12/06/2016

Fringe Width (w)=(lamda X D)/(slit seperation=2d) wher D is seperation b/w plane of slits and screen. therefore 2d=(lamda X D)/w. but for large values of D, angular width (theta in radians)= w/D. Hence finally 2d=lamda/(theta in radians). substituting the given values we get 2d=0.34 mm

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Dr K Venkateswarlu replied | 12/06/2016

Spacing b/w two slits (2d)= (lamda)/(theta in radians), where theta is angular width in radians. So substituting the given values, 2d= 0.34 mm

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Sajini 10/05/2016 in  IIT JEE Coaching classes

Show previous answers

Chaitanya replied | 10/05/2016

These are impure semiconductors . When a small quantity of impurity is mixed in a pure or intrinsic conductor , conductivity of semiconductor increases . Such an impure semiconductor is called extrinsic semiconductor

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U.k. replied | 11/05/2016

Intrinsic Semiconductor :
1.)These are pure semiconductor without any significant dopant species present. it is also called i-type semicondoctor. The number of charge carriers is therefore determined by the properties of the material itself instead of the amount of impurities.
2.) Conductivity of intrinsic semiconductors is poor .
3.) Number of electrons in conduction...  more»
Intrinsic Semiconductor :
1.)These are pure semiconductor without any significant dopant species present. it is also called i-type semicondoctor. The number of charge carriers is therefore determined by the properties of the material itself instead of the amount of impurities.
2.) Conductivity of intrinsic semiconductors is poor .
3.) Number of electrons in conduction band and holes in valence band are approximately equal .
4.) Fermi energy level lies at the centre of forbidden energy gap.

Extrinsic Semiconductors :
1.) These are impure semiconductors . When a small quantity of impurity is mixed in a pure or intrinsic conductor , conductivity of semiconductor increases . Such an impure semiconductor is called extrinsic semiconductor.
2.) Conductivity of extrinsic semiconductors is large.
3.) If it is an n-type semiconductor , electrons are majority carrier and holes are minority carrier and if it is a p-type semiconductor ,holes are majority carrier and electrons are minority carrier.
4.) In n-type semiconductor,Fermi-level lies near the bottom of conductioin band and in p-type semiconductor, fermi - level lies near the top of valence band . «less

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