Physics

This is a Short Answer Type Questions as classified in NCERT Exemplar

Explanation- Alloys are used for making standard resistance coil because they have low temperature coefficient of resistance with less temperature sensitivity. The alloys also have high resistivity and hence high resistance, because for given length and cross-section area of conductor .

This is a multiple choice answer as classified in NCERT Exemplar

(c) As we know PV =constant

Hence we can say that gas is going through an isothermal process.

Clearly from the graph that between process 1 and 2 temperature is constant and the gas expands and pressure decreases. So density of 2 is less than 1 so option ii

This is a Short Answer Type Questions as classified in NCERT Exemplar

Explanation- For the selection of metal for wiring in home the main criterion are: the availability, conductivity and the cost of the metal. The Cu wires or Al wires are used  for wiring in the home. The main considerations are involved in this process are cost of metal and good conductivity of metal.

This is a Short Answer Type Questions as classified in NCERT Exemplar

Explanation- Metallic strips have negligible resistance and need not to be counted in the length l₁, of the null point of potentiometer. That's why the thick metallic strips are used in potentiometer. It is for the convenience of experimenter as he measures only their lengths along the straight segments each of lengths 1 m.

This is a multiple choice answer as classified in NCERT Exemplar

(a) Amount of sweat evaporated /minute = $\frac{\frac{sweatproduced}{minute}}{numberofcaloriesrequiredforevaporation\frac{}{kg}}$

 = $\frac{14.5*{10}^3}{580*{10}^3}=0.25kg$

This is a multiple choice answer as classified in NCERT Exemplar

(c) For the curve 1 volume is constant so it is isochoric process. But in curve 2 and 3 curve 2 is steeper so 2 is adiabatic and 3 is isothermal.

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

process 1 isochoric and process 2 is isothermal .

Since, work done = area under P-V curve . here area under the pV curve 1 is more . so work done is more when the gas expands in isochoric process.

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

Coefficient of $\beta =5$

T₁= 27+273=300K

Coefficient of performance $\beta =\frac{T_2}{300-T_2}$

1500-5T₂=T₂

6T₂=1500

T₂= 250K

T₂= 250-273=-23^oC

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

Temperature of the source is 27⁰C

T₁= 27+273= 300K

T₂= -3+273= 270K

Efficiency of heat engine = 1-T₂/T₁= 1-270/300=1/10

Efficiency of refrigerator  is 50% of a perfect engine

= 0.5 $*\eta$ = 1/20

Coefficient of performance of the refrigerator $\beta =\frac{Q_2}{W}=\frac{1-{\eta }^{\text{'}}}{\eta }$

= $\frac{1-1/20}{1/20}=\frac{19/20}{1/20}=19$

Q₂= $\beta W$ =19W

= 19 $*$ 1KW=19KW= 19kJ/s