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Page 2 Solution: From the graph is clear that this is an isobaric process. P= constant At constant pressure W = nR?T … (1) ?Q=nC p?T (for constant pressure) 5 Q n R T ...(1) 2 ?? ? ? ? ?? ?? Equation (1)/(2) nR T 2 5 5 n R T 2 ? ?? ?? ? ?? ?? Q 2. The fundamental frequency in an open organ pipe is equal to the third harmonic of a closed organ pipe if the length of the closed organ pipe is 20 cm, the length of the open organ pipe is Option A 12.5 cm Option B 8 cm Option C 13.2 cm Option D 16 cm Correct Option C Solution: For open organ pipe open 2 2 nv General formula f= 2l vv f 2 ? ? ? ? ? ?? ? For pipe closed at one end General formula nv f= 4l Fundamental v f 4 ? Page 3 Solution: From the graph is clear that this is an isobaric process. P= constant At constant pressure W = nR?T … (1) ?Q=nC p?T (for constant pressure) 5 Q n R T ...(1) 2 ?? ? ? ? ?? ?? Equation (1)/(2) nR T 2 5 5 n R T 2 ? ?? ?? ? ?? ?? Q 2. The fundamental frequency in an open organ pipe is equal to the third harmonic of a closed organ pipe if the length of the closed organ pipe is 20 cm, the length of the open organ pipe is Option A 12.5 cm Option B 8 cm Option C 13.2 cm Option D 16 cm Correct Option C Solution: For open organ pipe open 2 2 nv General formula f= 2l vv f 2 ? ? ? ? ? ?? ? For pipe closed at one end General formula nv f= 4l Fundamental v f 4 ? As given: 1 2 2 3v v 3 1 4l 2l 4 20 2l 13.2 ? ? ? ? ? Q 3. The efficiency of an ideal heat engine working between the freezing point and boiling point of water, is Option A 6.25% Option B 20% Option C 26.8% Option D 12.5% Correct Option C Solution: Efficiency of heat engine 12 12 1 2 1 Q W Q work done Efficiency Energy available QQ Q T h1 T 273 1 373 1 0.731 26.8% ?? ? ? ?? ?? ?? ?? Q 4. At what temperature will the rms speed of oxygen molecules become just sufficient for escape from the Earth's atmosphere? (Given: Mass of oxygen molecule (m) = 2.76×10 -26 kg Option A 5.016×10 4 K Option B 8.360×10 4 K Option C 2.508×10 4 K Option D 1.254×10 4 K Correct Option B Solution: Escape velocity=11.2km/s=11200m/s 0 3 rms RT V M ? ? ? 23 2 3 26 30 1.38 10 T 11.2 10 2.76 10 ? ? ? ? ? ? ?? ? T = 8.360 ×10 4 Page 4 Solution: From the graph is clear that this is an isobaric process. P= constant At constant pressure W = nR?T … (1) ?Q=nC p?T (for constant pressure) 5 Q n R T ...(1) 2 ?? ? ? ? ?? ?? Equation (1)/(2) nR T 2 5 5 n R T 2 ? ?? ?? ? ?? ?? Q 2. The fundamental frequency in an open organ pipe is equal to the third harmonic of a closed organ pipe if the length of the closed organ pipe is 20 cm, the length of the open organ pipe is Option A 12.5 cm Option B 8 cm Option C 13.2 cm Option D 16 cm Correct Option C Solution: For open organ pipe open 2 2 nv General formula f= 2l vv f 2 ? ? ? ? ? ?? ? For pipe closed at one end General formula nv f= 4l Fundamental v f 4 ? As given: 1 2 2 3v v 3 1 4l 2l 4 20 2l 13.2 ? ? ? ? ? Q 3. The efficiency of an ideal heat engine working between the freezing point and boiling point of water, is Option A 6.25% Option B 20% Option C 26.8% Option D 12.5% Correct Option C Solution: Efficiency of heat engine 12 12 1 2 1 Q W Q work done Efficiency Energy available QQ Q T h1 T 273 1 373 1 0.731 26.8% ?? ? ? ?? ?? ?? ?? Q 4. At what temperature will the rms speed of oxygen molecules become just sufficient for escape from the Earth's atmosphere? (Given: Mass of oxygen molecule (m) = 2.76×10 -26 kg Option A 5.016×10 4 K Option B 8.360×10 4 K Option C 2.508×10 4 K Option D 1.254×10 4 K Correct Option B Solution: Escape velocity=11.2km/s=11200m/s 0 3 rms RT V M ? ? ? 23 2 3 26 30 1.38 10 T 11.2 10 2.76 10 ? ? ? ? ? ? ?? ? T = 8.360 ×10 4 Q 5. Unpolarised light is incident from air on a plane surface of a material of refractive index 'µ'. At a particular angle of incidence 'i', it is found that the reflected and refracted rays are perpendicular to each other, which of the following options is correct for this situation? Option A i = sin -1 1 ?? ?? ? ?? Option B Reflected light is polarised with its electric vector perpendicular to the plane of incidence Option C Reflected light is polarised with its electric vector parallel to the plane of incidence Option D i = tan -1 1 ?? ?? ? ?? Correct Option B Solution: This is the condition of polarisation in which light is incident on an interface at Brewster's angle. Thus reflected light is polarised with its E perpendicular to the plane of incidence. Q 6. In Young's double slit experiment the separation d between the slits is 2mm, the wavelength ? of the light used is 5896 Å and distance D between the screen and slits is 100 cm. It is found that the angular width of the fringes is 0.20°. To increase the fringe angular width to 0.21° (with same ? and D) the separation between the slits needs to be changed to Option A 2.1 mm Option B 1.9 mm Option C 1.8 mm Option D 1.7 mm Correct Option B Solution: Angular width = d d For new seperation ' d' ? ? ? ?? ? ?? Page 5 Solution: From the graph is clear that this is an isobaric process. P= constant At constant pressure W = nR?T … (1) ?Q=nC p?T (for constant pressure) 5 Q n R T ...(1) 2 ?? ? ? ? ?? ?? Equation (1)/(2) nR T 2 5 5 n R T 2 ? ?? ?? ? ?? ?? Q 2. The fundamental frequency in an open organ pipe is equal to the third harmonic of a closed organ pipe if the length of the closed organ pipe is 20 cm, the length of the open organ pipe is Option A 12.5 cm Option B 8 cm Option C 13.2 cm Option D 16 cm Correct Option C Solution: For open organ pipe open 2 2 nv General formula f= 2l vv f 2 ? ? ? ? ? ?? ? For pipe closed at one end General formula nv f= 4l Fundamental v f 4 ? As given: 1 2 2 3v v 3 1 4l 2l 4 20 2l 13.2 ? ? ? ? ? Q 3. The efficiency of an ideal heat engine working between the freezing point and boiling point of water, is Option A 6.25% Option B 20% Option C 26.8% Option D 12.5% Correct Option C Solution: Efficiency of heat engine 12 12 1 2 1 Q W Q work done Efficiency Energy available QQ Q T h1 T 273 1 373 1 0.731 26.8% ?? ? ? ?? ?? ?? ?? Q 4. At what temperature will the rms speed of oxygen molecules become just sufficient for escape from the Earth's atmosphere? (Given: Mass of oxygen molecule (m) = 2.76×10 -26 kg Option A 5.016×10 4 K Option B 8.360×10 4 K Option C 2.508×10 4 K Option D 1.254×10 4 K Correct Option B Solution: Escape velocity=11.2km/s=11200m/s 0 3 rms RT V M ? ? ? 23 2 3 26 30 1.38 10 T 11.2 10 2.76 10 ? ? ? ? ? ? ?? ? T = 8.360 ×10 4 Q 5. Unpolarised light is incident from air on a plane surface of a material of refractive index 'µ'. At a particular angle of incidence 'i', it is found that the reflected and refracted rays are perpendicular to each other, which of the following options is correct for this situation? Option A i = sin -1 1 ?? ?? ? ?? Option B Reflected light is polarised with its electric vector perpendicular to the plane of incidence Option C Reflected light is polarised with its electric vector parallel to the plane of incidence Option D i = tan -1 1 ?? ?? ? ?? Correct Option B Solution: This is the condition of polarisation in which light is incident on an interface at Brewster's angle. Thus reflected light is polarised with its E perpendicular to the plane of incidence. Q 6. In Young's double slit experiment the separation d between the slits is 2mm, the wavelength ? of the light used is 5896 Å and distance D between the screen and slits is 100 cm. It is found that the angular width of the fringes is 0.20°. To increase the fringe angular width to 0.21° (with same ? and D) the separation between the slits needs to be changed to Option A 2.1 mm Option B 1.9 mm Option C 1.8 mm Option D 1.7 mm Correct Option B Solution: Angular width = d d For new seperation ' d' ? ? ? ?? ? ?? 0.20 d' 0.21 d 0.20 d' 0.21 2 d' 1.904 ?? ?? ?? Q 7. An astronomical refracting telescope will have large angular magnification and high angular resolution, when it has an objective lens of Option A large focal length and large diameter Option B large focal length and small diameter Option C small focal length and large diameter Option D small focal length and small diameter Correct Option A Solution: R. P ? d 0 e f angular magnification= f And Aperture of objective Resolving power wavelength ? ? Greater the focal length of the objective, more is the magnification. Also for a telescope to have high resolution the aperture of objective lens should be large. Q 8. The kinetic energies of a planet in an elliptical orbit about the Sun, at positions A, B and C are K A, K B and K C, respectively. AC is the major axis and SB is perpendicular to AC at the position of the Sun S as shown in the figure. Then Option A K B<K A<K C Option B K A>K B>K C Option C K A<K B<K C Option D K B>K A>K C Correct Option B Solution: We know that angular momentum remains conserved In motion of a planet around the sun ? ? m r×v =constant The nearest point in perigee which is point A. Next nearest is B and then C Therefore V A B C VV ?? ? K A>K B>K CRead More
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