Page 1 CBSE XII | PHYSICS Board Paper – 2019 Solution CBSE Class XII Physics Board Paper – 2019 Solution SECTION – A 1. Plot of resistivity versus temperature for a typical semiconductor: 2. Attenuation: The loss of strength of a signal propagating through a medium is known as attenuation. 3. Sphere A will be negatively charged and sphere B will be positively charged. OR As the negatively charged rod is brought near the metallic sphere, the positive charges accumulate at the near end and the electron moves towards the farther end. When we earth the sphere, the electrons flow to the ground and the sphere becomes positively charged. 4. ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?? ? ? ? new new new new h KE KE 2h 2h KE h 2h KE h KE 2 h If the frequency of incident radiation doubles, the new kinetic energy will be more than double. Page 2 CBSE XII | PHYSICS Board Paper – 2019 Solution CBSE Class XII Physics Board Paper – 2019 Solution SECTION – A 1. Plot of resistivity versus temperature for a typical semiconductor: 2. Attenuation: The loss of strength of a signal propagating through a medium is known as attenuation. 3. Sphere A will be negatively charged and sphere B will be positively charged. OR As the negatively charged rod is brought near the metallic sphere, the positive charges accumulate at the near end and the electron moves towards the farther end. When we earth the sphere, the electrons flow to the ground and the sphere becomes positively charged. 4. ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?? ? ? ? new new new new h KE KE 2h 2h KE h 2h KE h KE 2 h If the frequency of incident radiation doubles, the new kinetic energy will be more than double. CBSE XII | PHYSICS Board Paper – 2019 Solution 5. ? 0 e 0e f m f on increasing f and decreasing f we can produce large magnification OR ? ? D= 1 1 And hence angle of minimum deviation also decreases. A As ? ? ? ? ? SECTION – B 6. After reflection from a convex mirror, the rays are diverging in nature and hence will never meet. Therefore, the convex mirror always gives a virtual and erect image. 7. Fission Fusion When neutrons are bombarded on a heavy nucleus, it splits into two nearly equal light fragments. At very high temperature and pressure, two light nuclei combine to form a heavy nucleus. Possible at ordinary temperature and pressure. Possible at very high temperature and pressure. Example: 1 235 144 89 1 0 92 56 36 0 n+ U 3 Ba Kr n ? ? ? Example: 1 1 2 1 1 1 0.42 H H H e v MeV ? ? ? ? ? ? 8. When an electron makes a transition from the second excited state to the first excited state: Page 3 CBSE XII | PHYSICS Board Paper – 2019 Solution CBSE Class XII Physics Board Paper – 2019 Solution SECTION – A 1. Plot of resistivity versus temperature for a typical semiconductor: 2. Attenuation: The loss of strength of a signal propagating through a medium is known as attenuation. 3. Sphere A will be negatively charged and sphere B will be positively charged. OR As the negatively charged rod is brought near the metallic sphere, the positive charges accumulate at the near end and the electron moves towards the farther end. When we earth the sphere, the electrons flow to the ground and the sphere becomes positively charged. 4. ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?? ? ? ? new new new new h KE KE 2h 2h KE h 2h KE h KE 2 h If the frequency of incident radiation doubles, the new kinetic energy will be more than double. CBSE XII | PHYSICS Board Paper – 2019 Solution 5. ? 0 e 0e f m f on increasing f and decreasing f we can produce large magnification OR ? ? D= 1 1 And hence angle of minimum deviation also decreases. A As ? ? ? ? ? SECTION – B 6. After reflection from a convex mirror, the rays are diverging in nature and hence will never meet. Therefore, the convex mirror always gives a virtual and erect image. 7. Fission Fusion When neutrons are bombarded on a heavy nucleus, it splits into two nearly equal light fragments. At very high temperature and pressure, two light nuclei combine to form a heavy nucleus. Possible at ordinary temperature and pressure. Possible at very high temperature and pressure. Example: 1 235 144 89 1 0 92 56 36 0 n+ U 3 Ba Kr n ? ? ? Example: 1 1 2 1 1 1 0.42 H H H e v MeV ? ? ? ? ? ? 8. When an electron makes a transition from the second excited state to the first excited state: CBSE XII | PHYSICS Board Paper – 2019 Solution ?? ?? ?? ? ?? 2 1 The wavelength of the emitted radiation when electron makes a transition from 2nd excited state to 1st excitded state 1 1 1 RZ 49 When electron makes transition from 1st excited state to ground st ?? ?? ?? ? ?? ? ? ? 2 2 1 2 ate 1 1 1 RZ 14 on solving 27 5 9. Because of symmetry, the forces 14 and F F , 25 and F F will cancel out each other and the effective force acting on the charge q ? would be 3 F . 2 3 2 kq F l ? OR 2 2 2 t=-qElsin? t=Ia ml a=-qElsin? -qElsin? a= ml -qE? a= ml -qE? -? ?= ml qE ?= ml ml T=2p qE Page 4 CBSE XII | PHYSICS Board Paper – 2019 Solution CBSE Class XII Physics Board Paper – 2019 Solution SECTION – A 1. Plot of resistivity versus temperature for a typical semiconductor: 2. Attenuation: The loss of strength of a signal propagating through a medium is known as attenuation. 3. Sphere A will be negatively charged and sphere B will be positively charged. OR As the negatively charged rod is brought near the metallic sphere, the positive charges accumulate at the near end and the electron moves towards the farther end. When we earth the sphere, the electrons flow to the ground and the sphere becomes positively charged. 4. ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?? ? ? ? new new new new h KE KE 2h 2h KE h 2h KE h KE 2 h If the frequency of incident radiation doubles, the new kinetic energy will be more than double. CBSE XII | PHYSICS Board Paper – 2019 Solution 5. ? 0 e 0e f m f on increasing f and decreasing f we can produce large magnification OR ? ? D= 1 1 And hence angle of minimum deviation also decreases. A As ? ? ? ? ? SECTION – B 6. After reflection from a convex mirror, the rays are diverging in nature and hence will never meet. Therefore, the convex mirror always gives a virtual and erect image. 7. Fission Fusion When neutrons are bombarded on a heavy nucleus, it splits into two nearly equal light fragments. At very high temperature and pressure, two light nuclei combine to form a heavy nucleus. Possible at ordinary temperature and pressure. Possible at very high temperature and pressure. Example: 1 235 144 89 1 0 92 56 36 0 n+ U 3 Ba Kr n ? ? ? Example: 1 1 2 1 1 1 0.42 H H H e v MeV ? ? ? ? ? ? 8. When an electron makes a transition from the second excited state to the first excited state: CBSE XII | PHYSICS Board Paper – 2019 Solution ?? ?? ?? ? ?? 2 1 The wavelength of the emitted radiation when electron makes a transition from 2nd excited state to 1st excitded state 1 1 1 RZ 49 When electron makes transition from 1st excited state to ground st ?? ?? ?? ? ?? ? ? ? 2 2 1 2 ate 1 1 1 RZ 14 on solving 27 5 9. Because of symmetry, the forces 14 and F F , 25 and F F will cancel out each other and the effective force acting on the charge q ? would be 3 F . 2 3 2 kq F l ? OR 2 2 2 t=-qElsin? t=Ia ml a=-qElsin? -qElsin? a= ml -qE? a= ml -qE? -? ?= ml qE ?= ml ml T=2p qE CBSE XII | PHYSICS Board Paper – 2019 Solution 10. Time taken by the particle to reduce to half of the initial number is half-life. Time taken by the particle to reduce to 0.37 of its initial value is called average life. 11. ? ?? ? ?? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 2 4 2 0 0 0 74 7 No of turns per unit length=10/cm=1000/m Area of cross section=1cm 1 10 m change in current=2-1=1A time taken=0.1seconds B= ni BA niA d di emf nA dt dt 1 emf 4 10 1000 1 10 0.1 emf 4 10 Wb OR ? ? ?? ? ? ? ? ? ? ? ? 4 3 NBA 140 0.09 5 10 6.3 10 Wb 12. Page 5 CBSE XII | PHYSICS Board Paper – 2019 Solution CBSE Class XII Physics Board Paper – 2019 Solution SECTION – A 1. Plot of resistivity versus temperature for a typical semiconductor: 2. Attenuation: The loss of strength of a signal propagating through a medium is known as attenuation. 3. Sphere A will be negatively charged and sphere B will be positively charged. OR As the negatively charged rod is brought near the metallic sphere, the positive charges accumulate at the near end and the electron moves towards the farther end. When we earth the sphere, the electrons flow to the ground and the sphere becomes positively charged. 4. ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?? ? ? ? new new new new h KE KE 2h 2h KE h 2h KE h KE 2 h If the frequency of incident radiation doubles, the new kinetic energy will be more than double. CBSE XII | PHYSICS Board Paper – 2019 Solution 5. ? 0 e 0e f m f on increasing f and decreasing f we can produce large magnification OR ? ? D= 1 1 And hence angle of minimum deviation also decreases. A As ? ? ? ? ? SECTION – B 6. After reflection from a convex mirror, the rays are diverging in nature and hence will never meet. Therefore, the convex mirror always gives a virtual and erect image. 7. Fission Fusion When neutrons are bombarded on a heavy nucleus, it splits into two nearly equal light fragments. At very high temperature and pressure, two light nuclei combine to form a heavy nucleus. Possible at ordinary temperature and pressure. Possible at very high temperature and pressure. Example: 1 235 144 89 1 0 92 56 36 0 n+ U 3 Ba Kr n ? ? ? Example: 1 1 2 1 1 1 0.42 H H H e v MeV ? ? ? ? ? ? 8. When an electron makes a transition from the second excited state to the first excited state: CBSE XII | PHYSICS Board Paper – 2019 Solution ?? ?? ?? ? ?? 2 1 The wavelength of the emitted radiation when electron makes a transition from 2nd excited state to 1st excitded state 1 1 1 RZ 49 When electron makes transition from 1st excited state to ground st ?? ?? ?? ? ?? ? ? ? 2 2 1 2 ate 1 1 1 RZ 14 on solving 27 5 9. Because of symmetry, the forces 14 and F F , 25 and F F will cancel out each other and the effective force acting on the charge q ? would be 3 F . 2 3 2 kq F l ? OR 2 2 2 t=-qElsin? t=Ia ml a=-qElsin? -qElsin? a= ml -qE? a= ml -qE? -? ?= ml qE ?= ml ml T=2p qE CBSE XII | PHYSICS Board Paper – 2019 Solution 10. Time taken by the particle to reduce to half of the initial number is half-life. Time taken by the particle to reduce to 0.37 of its initial value is called average life. 11. ? ?? ? ?? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 2 4 2 0 0 0 74 7 No of turns per unit length=10/cm=1000/m Area of cross section=1cm 1 10 m change in current=2-1=1A time taken=0.1seconds B= ni BA niA d di emf nA dt dt 1 emf 4 10 1000 1 10 0.1 emf 4 10 Wb OR ? ? ?? ? ? ? ? ? ? ? ? 4 3 NBA 140 0.09 5 10 6.3 10 Wb 12. CBSE XII | PHYSICS Board Paper – 2019 Solution Effective capacitance of both 3 F ? capacitors is 6 F ? and that for ?? 1 F and 2 F capacitors is ? 3F . Effective capacitance of the entire circuit 4 F ? . Energy stored is given by 2 2 CV ? ? ?? 2 4 4 100 2 2 10 J 0.02J SECTION – C 13. Effective resistance of the circuit is 8 ?. V = 16 V V=IR 16=I×8 I=2A current in the each branch is 1A so potential difference across 4O is given by V=1×4=4V 14. When the capacitor is connected to the battery, the charges starts accumulating on the plates of the capacitor. This process continues till the potential of the battery becomes equal to the battery. Because of this flow of charges the galvanometer shows deflection. E 00 1 Q Q F = E A= A= e A e If charge Q on the capacitor changes with time, there is a current dQ i dt ? ?? ?? ?? ?? ?? E 00 dF d Q 1 dQ dt dt dt ?? ? ? ? ?? ?? E d0 dF i dt where d I is the conduction currentRead More

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