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7 months ago

Physics Physics NCERT Exemplar Solutions Class 12th Chapter Three

Consider a simple circuit shown in figure stands for a variable resistance R'. R' can vary from R₀to infinity, r is internal resistance of the battery (r <(a) Potential drop across AB is nearly constant as R' is varied.
(b) Current through R' is nearly a constant as R' is varied.
(c) Current I depends sensitively on R'
(d) I ≥ V/r + R always;

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alok kumar singh

Contributor-Level 10

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer – (a, d)

Explanation- potential drop across AB is independent to R' also when we decrease the value of R the current will also very large. According to the relation I=e/R+r

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7 months ago

Physics Physics NCERT Exemplar Solutions Class 12th Chapter Three

Kirchhoff's junction rule is a reflection of
(a) Conservation of current density vector.
(b) Conservation of charge.
(c) The fact that the momentum with which a charged particle approaches a junction is unchanged (as a vector) as the charged particle leaves the junction.
(d) The fact that there is no accumulation of charges at a junction.

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alok kumar singh

Contributor-Level 10

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer – (b, d)

Explanation-Algebraic sum of the currents flowing towards any point in an electric network is zero. It also tell us about the conservation of charge.

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7 months ago

Physics Physics NCERT Exemplar Solutions Class 11th Chapter Thirteen

The volume of a given mass of a gas at 27°C, 1 atm is 100 cc. What will be its volume at 327°C?

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Payal Gupta

Contributor-Level 10

This is a short answer type question as classified in NCERT Exemplar

V $\propto T$

V/T = constant

$\frac{V_{1}}{T_{1}} = \frac{V_{2}}{T_{2}}$

T₁=273+27=300K

T₂= 273+327= 600K

V₁= 100cc

V₂=V₁ (600/300)

V₂=2V₁

V₂= 2 (100)=200cc

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7 months ago

Physics Physics NCERT Exemplar Solutions Class 12th Chapter Three

Which of the following characteristics of electrons determines the current in a conductor?
(a) Drift velocity alone
(b) Thermal velocity alone
(c) Both drift velocity and thermal velocity
(d) Neither drift nor thermal velocity

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alok kumar singh

Contributor-Level 10

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer- (a)

Explanation- I=AneV_d , current is directly proportional to drift velocity.

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7 months ago

Physics Physics NCERT Exemplar Solutions Class 11th Chapter Thirteen

The volume of a given mass of a gas at 27°C, 1 atm is 100 cc. What will be its volume at 327°C?

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New answer posted

7 months ago

Physics Physics NCERT Exemplar Solutions Class 12th Chapter Three

A metal rod of length 10 cm and a rectangular cross-section of 1 cm x 1/2 cm is connected to a battery across opposite faces. The resistance will be
(a) Maximum when the battery is connected across 1 cm x 1/2 cm faces
(b) Maximum when the battery is connected across 10 cm x 1 cm faces
(c) Maximum when the battery is connected across 10 cm x 1/2 cm faces
(d) Same irrespective of the three faces

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alok kumar singh

Contributor-Level 10

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer- (a)

Explanation- R= $\frac{δ l}{A}$ for greater value of R, A should be less and its possible value when connected across 1cm $*$ 1/2cm faces.

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7 months ago

Physics Physics NCERT Exemplar Solutions Class 11th Chapter Thirteen

Calculate the number of atoms in 39.4 g gold. Molar mass of gold is 197g mole^-1.

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Payal Gupta

Contributor-Level 10

This is a short answer type question as classified in NCERT Exemplar

molar mass = mass of avogadro's number of atoms= 6.023 $* 10^{23}$ atoms.

197 g of gold contains =6.023 $* 10^{23} a t o m s$

1g of gold contain= $\frac{6.023 * 10^{23}}{197}$ atoms

39.4 g of gold atoms = $\frac{6.023 * 10^{23} * 39.4}{197} = 1.2 * 10^{23}$ atoms

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7 months ago

Physics Physics NCERT Exemplar Solutions Class 12th Chapter Three

Two cells of emfs approximately 5 V and 10 V are to be accurately compared using a potentiometer of length 400 cm.4.
(a) The battery that runs the potentiometer should have voltage of 8 V.
(b) The battery of potentiometer can have a voltage of 15 V and R adjusted so that the potential drop across the wire slightly exceeds 10 V.

(c) The first portion of 50 cm of wire itself should have a potential drop of 10 V.
(d) Potentiometer is usually used for comparing resistances and not voltages.

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alok kumar singh

Contributor-Level 10

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer- (b)

Explanation-The potential drop along the wires of potentiometer should be greater than emfs of cells.
In a potentiometer experiment, the emf of a cell can be measured if the potential drop along the potentiometer wire is more than the emf of the cell to be determined. Here, values of emfs of two cells are given as 5 V and 10 V, therefore, the potential drop along the potentiometer wire must be more than 10 V.

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7 months ago

Physics Physics NCERT Exemplar Solutions Class 12th Chapter Three

A resistance R is to be measured using a meter bridge, a student chooses the standard resistance S to be 100 Ω He finds the null point at l₁= 2.9 cm. He is told to attempt to improve the accuracy. Which of the following is a useful way?
(a) He should measure l₁, more accurately
(b) He should change S to 1000 ? and repeat the experiment
(c) He should change S to 3 ? and repeat the experiment
(d) He should have given up hope of a more accurate measurement with a meter bridge.

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alok kumar singh

Contributor-Level 10

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer – (c)

Explanation – R/S= (l₁/100-l₁)= 100 (2.9/100-2.9)= 100/97.1=2.98ohm

So he should change S to almost 3 ohm and repeat the experiment.

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7 months ago

Physics Physics NCERT Exemplar Solutions Class 11th Chapter Thirteen

Consider a rectangular block of wood moving with a velocity v₀ in a gas at temperature T and mass density ρ. Assume the velocity is along x-axis and the area of cross-section of the block perpendicular to v₀ is A. Show that the drag force on the block is 4ρ 0 kT Av m , where m is the mass of the gas molecule

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Payal Gupta

Contributor-Level 10

This is a long answer type question as classified in NCERT Exemplar

Consider the diagram

let n =number of molecules per unit volume

V_rms= rms speed of gas molecule

When block is moving with speed v_o,relative speed of molecules w.r.t front face =v+v_o

Coming head on, momentum transferred to block per collision =2m (v+v_o)

Number of collisions in time $? t$ = $\frac{1}{2}$ (v+v_o)n $? t$ A where A is the area of cross section.

So momentum transferred in time $? t$ =m (v+v_o)²nA $? t$ this is from front surface

Similarly momentum transferred in time $? t$ = m (v-v_o)²nA $? t$ ) this is from back surface

Drag force = mnA (v+v_o)²- (v-v_o)²)

= mnA (4w_o)=4mnAvv_o

= 4 $ρ A$ vv_o

So $ρ$ =mn/V=M/

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This is a long answer type question as classified in NCERT Exemplar

Consider the diagram

let n =number of molecules per unit volume

V_rms= rms speed of gas molecule

When block is moving with speed v_o,relative speed of molecules w.r.t front face =v+v_o

Coming head on, momentum transferred to block per collision =2m (v+v_o)

Number of collisions in time $? t$ = $\frac{1}{2}$ (v+v_o)n $? t$ A where A is the area of cross section.

So momentum transferred in time $? t$ =m (v+v_o)²nA $? t$ this is from front surface

Similarly momentum transferred in time $? t$ = m (v-v_o)²nA $? t$ ) this is from back surface

Drag force = mnA (v+v_o)²- (v-v_o)²)

= mnA (4w_o)=4mnAvv_o

= 4 $ρ A$ vv_o

So $ρ$ =mn/V=M/V

If v = velocity along x axis

Then we can write KE= ½ mv²=1/2 K_BT

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