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Recent questions in Physics
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CBSE XII
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Physics
Physics
Electric charges and fields
Electrostatic Potential and Capacitance
Current Electricity
Moving charges and magnetism
Magnetism and matter
Electromagnetic induction
Alternating current
Electromagnetic waves
Ray optics and optical instruments
Wave optics
Dual nature of radiation and matter
Atoms
Nuclei
Semiconductor electronics
Communication systems
An electric kettle has two coils. When one of these is switched on, the water in the kettle boils in 6 minutes. When the other coil is switched on, the water boils in 3 minutes. If the two coils are connected in series , find the time taken to boil the water in the kettle .
cbse
class12
physics
ch-3
sec-a
q99
medium
asked
Jul 3, 2015
by
meena.p
1
answer
An immersion heater is rated $836 walt$ In what time it should heat litre of water from $20^{\circ}$ to $40^{\circ}? J= 4.18 \;J/cal $
cbse
class12
physics
ch-3
sec-a
q98
medium
asked
Jul 3, 2015
by
meena.p
1
answer
The earth's surface has a negative surface charge density of $ 10^{-9}cm^{-2}$. The potential difference of $400\;kv$ between the top of the atmosphere and the surface results (due to low conductivity of the lower atmosphere ) in a current of only $1800\;A$ over the entire globe. If their were no mechanism of sustaining atmosphere field, how much time (roughly) would be required to neutralise the the earth's surface ? (This never happen in practice became there is a mechanism to replenish electric charges namely the continual thunder storms and lighting in different parts of the globe) . Radius of the earth $=6.37 \times 10^6m$
cbse
class12
physics
ch-3
sec-a
q97
medium
asked
Jul 3, 2015
by
meena.p
1
answer
Which of the following : characteristic of electrons . determines the current in a conductor ?
cbse
class12
physics
ch-3
sec-a
q95
easy
asked
Jul 3, 2015
by
meena.p
1
answer
A metal rod of length $10\;cm$ and a rectangular . Cross section of $1 \;cm \times \large\frac{1}{2}$$\;cm$ is connected to a battery across opposite faces. The resistance will be
cbse
class12
physics
ch-3
sec-a
q94
easy
asked
Jul 3, 2015
by
meena.p
1
answer
Given resistance of $1 \Omega, 2 \Omega$ and $3 \Omega$ how will we combined them to get an equivalent resistance of $\large\frac{6}{11}$$ \Omega$
cbse
class12
physics
ch-3
sec-a
q87
easy
asked
Jul 3, 2015
by
meena.p
1
answer
Given resistance of $1 \Omega, 2 \Omega$ and $3 \Omega$ how will we combined them to get an equivalent resistance of $6 \Omega$
cbse
class12
physics
ch-3
sec-a
q86
easy
asked
Jul 3, 2015
by
meena.p
1
answer
Given n resistor each resistance R, What is the ratio of the maximum to minimum resistance ?
cbse
class12
physics
ch-3
sec-a
q83
easy
asked
Jul 3, 2015
by
meena.p
1
answer
Given n resistance R, how will you combine them to get the minimum effective resistance ?
cbse
class12
physics
ch-3
sec-a
q82
easy
asked
Jul 3, 2015
by
meena.p
1
answer
Given n resistor each resistance R, how will you combine them to get the maximum effective resistance ?
cbse
class12
physics
ch-3
sec-a
q81
easy
asked
Jul 3, 2015
by
meena.p
1
answer
The resistivity of a typical insulator (eg: amber) is greater than that of a metal by a factor of the order of ____$(10^{22}/10^{23})$
cbse
class12
physics
ch-3
sec-a
q80
easy
asked
Jul 2, 2015
by
meena.p
1
answer
The resistivity of the alloy mangain is nearly ____(independent of /increase rapidly) with increase of temperature
cbse
class12
physics
ch-3
sec-a
q79
easy
asked
Jul 2, 2015
by
meena.p
1
answer
Choose the correct alternative: Alloys usually have must ______( lower/higher ) temperature coefficients of resistance than pure metals
cbse
class12
physics
ch-3
sec-a
q78
easy
asked
Jul 2, 2015
by
meena.p
1
answer
Choose the correct alternative : Alloys of metals usually have___________ (greater / lesser) resistivity than that of their constituent metals
cbse
class12
physics
ch-3
sec-a
q77
easy
asked
Jul 2, 2015
by
meena.p
1
answer
A high tension (HT) supply of say $6kv$ must have a very large internal resistance . Why ?
cbse
class12
physics
ch-3
sec-a
q76
easy
asked
Jul 2, 2015
by
meena.p
1
answer
A low voltage supply from which one needs high currents must have low internal resistance why ?
cbse
class12
physics
ch-3
sec-a
q75
easy
asked
Jul 2, 2015
by
meena.p
1
answer
Is Ohm's law universally applicable for all conducting elements? If not give examples of elements which do not obey ohm's law
cbse
class12
physics
ch-3
sec-a
q74
easy
asked
Jul 2, 2015
by
meena.p
1
answer
A steady current flow in a metallic conductor of non - uniform cross - section which of these quantities is constant along the conductor
cbse
class12
physics
ch-3
sec-a
q73
easy
asked
Jul 2, 2015
by
meena.p
1
answer
Explain why aluminium Wires are preferred for overhead power cables?
cbse
class12
physics
ch-3
sec-a
q72
easy
asked
Jul 2, 2015
by
meena.p
1
answer
Two wires of equal lengths , One of aluminium and the other of copper have the same resistance . Which of the two wires is lighter. $[\rho_A =2.63 \times 10^{-8} \Omega m, \rho_{cn}= 1.72 \times 10^{-8} \Omega -m$. Relative density of $Al =2.7$ , Relative density of $Cu= 8.9 ]$
cbse
class12
physics
ch-3
sec-a
q71
difficult
asked
Jul 2, 2015
by
meena.p
1
answer
A secondary cell after long use has an emt of $1.9\;V$ and a large internal resistance of $ 380 \Omega$ What maximum current can be drawn from the cell ?
cbse
class12
physics
ch-3
sec-a
q70
medium
asked
Jul 1, 2015
by
meena.p
1
answer
Six lead acid type of secondary cells each of emf $2.0V$ and internal resistance $0.015\Omega$ are joined in series to provide a supply to a resistance of $8.5 \Omega$ What are the current drawn from the supply and its terminal voltage ?
cbse
class12
physics
ch-3
sec-b
q69
medium
asked
Jul 1, 2015
by
meena.p
1
answer
What is the purpose of having a series resistor in the charging circuits?
cbse
class12
physics
ch-3
sec-a
q68
easy
asked
Jul 1, 2015
by
meena.p
1
answer
A storage battery of emf $8.0 V$ and internal resistance $0.5 \Omega$ is being changed by a $120\;V$ DC supply using a series resistor of $15. 5 \Omega$ What is the terminal voltage of the battery during changing ?
cbse
class12
physics
ch-3
sec-b
q67
medium
asked
Jul 1, 2015
by
meena.p
1
answer
The number of density of free electron in a copper conductor estimated at $8.5 \times 10^{20}m^{-3}$. How long does an electron take a drift from one end of a wire $3.0 \; m$ long to its other end ? The area of cross - section of the wire is $2 \times 10^{-6}\;m^2$ and it is carrying of $3.0 \;A$
cbse
class12
physics
ch-3
sec-b
q66
difficult
asked
Jul 1, 2015
by
meena.p
1
answer
In a potentiometer arrangement, a cell of emt $1.25\;V$ gives a balance point at $35. 0\;cm$ length of the wire. If the cell is replaced by another cell and the balance point shifts $63.0\;cm$, What is the emf of the second cell ?
cbse
class12
physics
ch-3
sec-b
q65
easy
asked
Jul 1, 2015
by
meena.p
1
answer
In a metre bridge , the balance point is found to be at $39.5\;cm$ from the end A, when the resistor Y is of $12.5 \;ohm$. Determine the resistance of x. Why are the connections between resistors in a metre bridge made of thick copper ships ? What happens if the galvanometer and cell are interchanged at the balanced point of the bridge ? would the galvanometer show any current?
cbse
class12
physics
ch-3
sec-b
q64
difficult
asked
Jul 1, 2015
by
meena.p
1
answer
Define the term electrical resistivity of a material. Write the S.I units. Derive an expression for the resistivity of a metal in terms of number density and mass of free electrons present in it .
cbse
class12
physics
ch-3
sec-b
q63
difficult
asked
Jul 1, 2015
by
meena.p
1
answer
What is the Potential gradient? How is it measured? Explain
cbse
class12
physics
ch-3
sec-b
q61
medium
asked
Jul 1, 2015
by
meena.p
1
answer
If the length of the wire be doubled, What will be effect on the position of zero deflection in a potentio meter ? Explain
cbse
class12
physics
ch-3
sec-b
q60
easy
asked
Jul 1, 2015
by
meena.p
1
answer
Kirchhoff's first law obeys rule of conservation of charge Explain
cbse
class12
physics
ch-3
sec-b
q59
medium
asked
Jun 30, 2015
by
meena.p
1
answer
How does the fuse wire save the electrical installation?
cbse
class12
physics
ch-3
sec-a
q58
easy
asked
Jun 30, 2015
by
meena.p
1
answer
By what percentage will have the illumination of amp decrease if the current drops by $20\%$ ?
cbse
class12
physics
ch-3
sec-b
q57
difficult
asked
Jun 30, 2015
by
meena.p
1
answer
A heating element using michrome connected to a $230\;V$ supply draws an initial current of $3.2 \;A$ Which settles after a few seconds to a steady value of $2.8 \;A$. What is the steady temperature of the heating element if the room temperature is $27.0^{\circ}$ ? Temperature coefficient of resistance of michrome averaged over the temperature range involved is $1.70 \times 10^{-4 \circ}C^{-1}$
cbse
class12
physics
ch-3
sec-a
q56
medium
asked
Jun 30, 2015
by
meena.p
1
answer
A silver wire has a resistance of $2.1 \Omega$ at $27.5^{\circ}C$ and a resistance of $2.7\Omega$ at $100^{\circ}$. Determine the temperature coefficient of resistivity of silver.
cbse
class12
physics
ch-3
sec-a
q54
easy
asked
Jun 30, 2015
by
meena.p
1
answer
At Room temperature $(27.0^{\circ})$ the resistance of a heating element is $100\;\Omega$ What is the temperature of the element if the resistance is found to be $117\;\Omega$ , given that the temperature coefficient of the material of the resistance is $1.70 \times 10^{-4} .c^{-1}$
cbse
class12
physics
ch-3
sec-a
q55
medium
asked
Jun 30, 2015
by
meena.p
1
answer
A negligibly small current is passed through a wire of length $15\;cm$ and uniform cross section wire of length $6.0 \times 10^{-7}\;m^2$ and its resistance is measured to be $5.0 \Omega$ What is the resistivity of the material at the temperature of the experiment ?
cbse
class12
physics
ch-3
sec-a
q53
easy
asked
Jun 30, 2015
by
meena.p
1
answer
The storage battery of a car has an emt of $12\;V$. If the interval resistance of a battery is $0.4 \Omega$, What is the maximum current that can be drawn from the battery ?
cbse
class12
physics
ch-3
sec-a
q51
easy
asked
Jun 30, 2015
by
meena.p
1
answer
A current in a circuit having constant resistance is tripled. How does this affect the power dissipation ?
cbse
class12
physics
ch-3
sec-a
q50
medium
asked
Jun 30, 2015
by
meena.p
1
answer
What are the factor does the potential gradient of the potentiometer wire depend ?
cbse
class12
physics
ch-3
sec-a
q48
medium
asked
Jun 30, 2015
by
meena.p
1
answer
What is potential gradient? State its SI unit
cbse
class12
physics
ch-3
sec-a
q46
medium
asked
Jun 30, 2015
by
meena.p
1
answer
What are the two practical forms of wheat stone bridge?
cbse
class12
physics
ch-3
sec-a
q45
easy
asked
Jun 30, 2015
by
meena.p
1
answer
A resistance R is connected across a cell of emf e and internal resistance r. A potentio meter now measures the potential difference between the terminals of the cell as V. Write an expression for r in terms of e, V and R.
cbse
class12
physics
ch-3
sec-a
q44
easy
asked
Jun 30, 2015
by
meena.p
1
answer
Why is meter bridge also called a slide wire bridge ?
cbse
class12
physics
ch-3
sec-a
q43
easy
asked
Jun 30, 2015
by
meena.p
1
answer
A current of $1.0\;mA$ s flowing through a potentio meter wire of length $4\;m$ and of resistance $4 \Omega$ ,find the potential gradient of the potentio meter wire .
cbse
class12
physics
ch-3
sec-a
q42
difficult
asked
Jun 30, 2015
by
meena.p
1
answer
When is the Wheatstones bridge most sensitive ?
cbse
class12
physics
ch-3
sec-a
q41
difficult
asked
Jun 30, 2015
by
meena.p
1
answer
Resistance of a human body is of the order of $10 \;k \Omega$ . Why does one experience a strong wire of say $240\;V$ supply ?
cbse
class12
physics
ch-3
sec-a
q40
difficult
asked
Jun 30, 2015
by
meena.p
1
answer
Why is the potential preferred over voltmeter for measuring e.m.f ?
cbse
class12
physics
ch-3
sec-a
q39
medium
asked
Jun 30, 2015
by
meena.p
1
answer
If P.d applied across a conductor is increased to $2V$ ,how will the drift velocity of the electrons change?
cbse
class12
physics
ch-3
sec-a
q38
difficult
asked
Jun 30, 2015
by
meena.p
1
answer
If the length of a wire conductor is doubled by stretching it, keeping the p.d across it constant, by what factor does the drift speed of electrons charge ?
cbse
class12
physics
ch-3
sec-a
q37
difficult
asked
Jun 30, 2015
by
meena.p
1
answer
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