Page 1 CBSE XII | PHYSICS Sample Paper – 4 Solution CBSE Board Class XII – Physics Sample Paper – 4 Solution 1. The proton A and the electron B will experience electrostatic force of equal magnitude but in opposite direction. 2. As mv r qB ? , for same v and B, . m r q ? Since m q is smaller for an electron, the radius of the circular path followed by the electron will be smaller. 3. The human eye is most sensitive for 14 5.405 10 . Hz ? 4. Induced current in the loop will be in the clockwise direction to oppose its origin. 5. Since ? ? 12 1 1 1 1 n f R R ?? ? ? ? ?? ?? Taking ? ? 12 21 1 ,, n R R R R fR ? ? ? ? ? …. (1) When lens is cut, then 12 11 ,, ' n R R R fR ? ? ? ? ? …..(2) Using equation (1) and equation (2), we get ' 2 60 f f cm ?? 6. No, matter waves are not electromagnetic waves. The de Broglie wave equation is ? ? h mv 7. A rectifier conducts only in forward biased and not in reverse biased. But a transistor conducts either ways. Hence, a transistor cannot be used as a rectifier. 8. The negative energy of the electron orbiting around nucleus keeps it bounded with the nucleus. If the energy of the electron becomes positive, the electron will no longer be bounded with the nucleus. Page 2 CBSE XII | PHYSICS Sample Paper – 4 Solution CBSE Board Class XII – Physics Sample Paper – 4 Solution 1. The proton A and the electron B will experience electrostatic force of equal magnitude but in opposite direction. 2. As mv r qB ? , for same v and B, . m r q ? Since m q is smaller for an electron, the radius of the circular path followed by the electron will be smaller. 3. The human eye is most sensitive for 14 5.405 10 . Hz ? 4. Induced current in the loop will be in the clockwise direction to oppose its origin. 5. Since ? ? 12 1 1 1 1 n f R R ?? ? ? ? ?? ?? Taking ? ? 12 21 1 ,, n R R R R fR ? ? ? ? ? …. (1) When lens is cut, then 12 11 ,, ' n R R R fR ? ? ? ? ? …..(2) Using equation (1) and equation (2), we get ' 2 60 f f cm ?? 6. No, matter waves are not electromagnetic waves. The de Broglie wave equation is ? ? h mv 7. A rectifier conducts only in forward biased and not in reverse biased. But a transistor conducts either ways. Hence, a transistor cannot be used as a rectifier. 8. The negative energy of the electron orbiting around nucleus keeps it bounded with the nucleus. If the energy of the electron becomes positive, the electron will no longer be bounded with the nucleus. CBSE XII | PHYSICS Sample Paper – 4 Solution 9. (i) water ? ? 2 HO (ii) oxygen ? ? 2 O The ratio of permittivity of a medium to the permittivity of vacuum is called dielectric constant for the medium. 10. Resistance = A ? 2 4 dr dR r ? ? ? ? Total resistance 2 2 2 1 1 1 44 r r r r dr rr ?? ?? ?? ? ? ? ?? ?? ? 12 11 4 R rr ? ? ?? ?? ?? ?? 11. When current flows through a solenoid, it flows in same direction in each turn as shown in the figure below. As current through each turn is in same direction, they attract each other. Hence, the solenoid contracts in length. Page 3 CBSE XII | PHYSICS Sample Paper – 4 Solution CBSE Board Class XII – Physics Sample Paper – 4 Solution 1. The proton A and the electron B will experience electrostatic force of equal magnitude but in opposite direction. 2. As mv r qB ? , for same v and B, . m r q ? Since m q is smaller for an electron, the radius of the circular path followed by the electron will be smaller. 3. The human eye is most sensitive for 14 5.405 10 . Hz ? 4. Induced current in the loop will be in the clockwise direction to oppose its origin. 5. Since ? ? 12 1 1 1 1 n f R R ?? ? ? ? ?? ?? Taking ? ? 12 21 1 ,, n R R R R fR ? ? ? ? ? …. (1) When lens is cut, then 12 11 ,, ' n R R R fR ? ? ? ? ? …..(2) Using equation (1) and equation (2), we get ' 2 60 f f cm ?? 6. No, matter waves are not electromagnetic waves. The de Broglie wave equation is ? ? h mv 7. A rectifier conducts only in forward biased and not in reverse biased. But a transistor conducts either ways. Hence, a transistor cannot be used as a rectifier. 8. The negative energy of the electron orbiting around nucleus keeps it bounded with the nucleus. If the energy of the electron becomes positive, the electron will no longer be bounded with the nucleus. CBSE XII | PHYSICS Sample Paper – 4 Solution 9. (i) water ? ? 2 HO (ii) oxygen ? ? 2 O The ratio of permittivity of a medium to the permittivity of vacuum is called dielectric constant for the medium. 10. Resistance = A ? 2 4 dr dR r ? ? ? ? Total resistance 2 2 2 1 1 1 44 r r r r dr rr ?? ?? ?? ? ? ? ?? ?? ? 12 11 4 R rr ? ? ?? ?? ?? ?? 11. When current flows through a solenoid, it flows in same direction in each turn as shown in the figure below. As current through each turn is in same direction, they attract each other. Hence, the solenoid contracts in length. CBSE XII | PHYSICS Sample Paper – 4 Solution 12. Due to the applied e.m.f. E, the current ‘I’ in the inductor will be such that: or dI E E L dI dt dt L ?? 00 sin or sin E t dt E dI I t dt LL ? ? ?? ? 0 cos E It L ? ? ?? 0 or sin 2 ?? ?? ?? ? ? I I t Where 0 0 E I L ? ? 13. Here 1 2 2 100 , 10 , 20 q q C r cm r cm ? ? ? ? ? Work done is 1 2 2 1 0 1 2 4 ?? ? ? ?? ?? ?? qq r r W rr ? ? 2 69 2 10 1 100 10 9 10 200 10 ? ? ?? ? ? ? ? ? ?? ?? 450 J ? 14. When light is put off, a large e.m.f. is produced to oppose the decay of current in the circuit. This large induced e.m.f. across the gap causes sparking in the switch. OR Iron bar experiences a retarding force. It means eddy currents are there, which are produced whenever there is a change in magnetic flux. So we conclude that iron bar is a magnet. 15. A stationary charge produces only an electric field around it. When a charge moves with a constant velocity it produces a constant magnetic field in addition to the electric field. As the charge is accelerated, both electric and magnetic fields change with time and space. One becomes the source of the other, thus giving electromagnetic waves. Page 4 CBSE XII | PHYSICS Sample Paper – 4 Solution CBSE Board Class XII – Physics Sample Paper – 4 Solution 1. The proton A and the electron B will experience electrostatic force of equal magnitude but in opposite direction. 2. As mv r qB ? , for same v and B, . m r q ? Since m q is smaller for an electron, the radius of the circular path followed by the electron will be smaller. 3. The human eye is most sensitive for 14 5.405 10 . Hz ? 4. Induced current in the loop will be in the clockwise direction to oppose its origin. 5. Since ? ? 12 1 1 1 1 n f R R ?? ? ? ? ?? ?? Taking ? ? 12 21 1 ,, n R R R R fR ? ? ? ? ? …. (1) When lens is cut, then 12 11 ,, ' n R R R fR ? ? ? ? ? …..(2) Using equation (1) and equation (2), we get ' 2 60 f f cm ?? 6. No, matter waves are not electromagnetic waves. The de Broglie wave equation is ? ? h mv 7. A rectifier conducts only in forward biased and not in reverse biased. But a transistor conducts either ways. Hence, a transistor cannot be used as a rectifier. 8. The negative energy of the electron orbiting around nucleus keeps it bounded with the nucleus. If the energy of the electron becomes positive, the electron will no longer be bounded with the nucleus. CBSE XII | PHYSICS Sample Paper – 4 Solution 9. (i) water ? ? 2 HO (ii) oxygen ? ? 2 O The ratio of permittivity of a medium to the permittivity of vacuum is called dielectric constant for the medium. 10. Resistance = A ? 2 4 dr dR r ? ? ? ? Total resistance 2 2 2 1 1 1 44 r r r r dr rr ?? ?? ?? ? ? ? ?? ?? ? 12 11 4 R rr ? ? ?? ?? ?? ?? 11. When current flows through a solenoid, it flows in same direction in each turn as shown in the figure below. As current through each turn is in same direction, they attract each other. Hence, the solenoid contracts in length. CBSE XII | PHYSICS Sample Paper – 4 Solution 12. Due to the applied e.m.f. E, the current ‘I’ in the inductor will be such that: or dI E E L dI dt dt L ?? 00 sin or sin E t dt E dI I t dt LL ? ? ?? ? 0 cos E It L ? ? ?? 0 or sin 2 ?? ?? ?? ? ? I I t Where 0 0 E I L ? ? 13. Here 1 2 2 100 , 10 , 20 q q C r cm r cm ? ? ? ? ? Work done is 1 2 2 1 0 1 2 4 ?? ? ? ?? ?? ?? qq r r W rr ? ? 2 69 2 10 1 100 10 9 10 200 10 ? ? ?? ? ? ? ? ? ?? ?? 450 J ? 14. When light is put off, a large e.m.f. is produced to oppose the decay of current in the circuit. This large induced e.m.f. across the gap causes sparking in the switch. OR Iron bar experiences a retarding force. It means eddy currents are there, which are produced whenever there is a change in magnetic flux. So we conclude that iron bar is a magnet. 15. A stationary charge produces only an electric field around it. When a charge moves with a constant velocity it produces a constant magnetic field in addition to the electric field. As the charge is accelerated, both electric and magnetic fields change with time and space. One becomes the source of the other, thus giving electromagnetic waves. CBSE XII | PHYSICS Sample Paper – 4 Solution 16. Image of the object is formed at focus of objective. This image acts like an object for virtual image of 1 L . Now virtual image produced by 1 L should be located at the focus of 2 . L Since 12 2 /3 L L f ? Image distance from 1 is /3 L v f ?? 1 1 1 f v u ? ? ? 1 3 1 f f u ? ? ? /4 uf ? ? ? 17. (i) Actual depth t =12.5 cm Apparent depth a = 9.4 cm 12.5 1.33 9.4 aw t a ? ? ? ? (ii) 1.63 al ? ? 12.5 7.7 1.63 l al t a cm ? ? ? ? Therefore, the microscope has to be moved by ? ? 9.4 7.7 , cm ? i.e., 1.7 cm 18. The capacitor can be considered as split into two capacitors in series as shown below Here, 1 2 0 12 22 o K A k A c and c dd ?? ?? The capacitance of capacitors in series is 12 1 1 1 c c c ?? 12 12 cc c cc ?? ? 12 12 2 o A kk c d k k ??? ? ?? ? ?? Page 5 CBSE XII | PHYSICS Sample Paper – 4 Solution CBSE Board Class XII – Physics Sample Paper – 4 Solution 1. The proton A and the electron B will experience electrostatic force of equal magnitude but in opposite direction. 2. As mv r qB ? , for same v and B, . m r q ? Since m q is smaller for an electron, the radius of the circular path followed by the electron will be smaller. 3. The human eye is most sensitive for 14 5.405 10 . Hz ? 4. Induced current in the loop will be in the clockwise direction to oppose its origin. 5. Since ? ? 12 1 1 1 1 n f R R ?? ? ? ? ?? ?? Taking ? ? 12 21 1 ,, n R R R R fR ? ? ? ? ? …. (1) When lens is cut, then 12 11 ,, ' n R R R fR ? ? ? ? ? …..(2) Using equation (1) and equation (2), we get ' 2 60 f f cm ?? 6. No, matter waves are not electromagnetic waves. The de Broglie wave equation is ? ? h mv 7. A rectifier conducts only in forward biased and not in reverse biased. But a transistor conducts either ways. Hence, a transistor cannot be used as a rectifier. 8. The negative energy of the electron orbiting around nucleus keeps it bounded with the nucleus. If the energy of the electron becomes positive, the electron will no longer be bounded with the nucleus. CBSE XII | PHYSICS Sample Paper – 4 Solution 9. (i) water ? ? 2 HO (ii) oxygen ? ? 2 O The ratio of permittivity of a medium to the permittivity of vacuum is called dielectric constant for the medium. 10. Resistance = A ? 2 4 dr dR r ? ? ? ? Total resistance 2 2 2 1 1 1 44 r r r r dr rr ?? ?? ?? ? ? ? ?? ?? ? 12 11 4 R rr ? ? ?? ?? ?? ?? 11. When current flows through a solenoid, it flows in same direction in each turn as shown in the figure below. As current through each turn is in same direction, they attract each other. Hence, the solenoid contracts in length. CBSE XII | PHYSICS Sample Paper – 4 Solution 12. Due to the applied e.m.f. E, the current ‘I’ in the inductor will be such that: or dI E E L dI dt dt L ?? 00 sin or sin E t dt E dI I t dt LL ? ? ?? ? 0 cos E It L ? ? ?? 0 or sin 2 ?? ?? ?? ? ? I I t Where 0 0 E I L ? ? 13. Here 1 2 2 100 , 10 , 20 q q C r cm r cm ? ? ? ? ? Work done is 1 2 2 1 0 1 2 4 ?? ? ? ?? ?? ?? qq r r W rr ? ? 2 69 2 10 1 100 10 9 10 200 10 ? ? ?? ? ? ? ? ? ?? ?? 450 J ? 14. When light is put off, a large e.m.f. is produced to oppose the decay of current in the circuit. This large induced e.m.f. across the gap causes sparking in the switch. OR Iron bar experiences a retarding force. It means eddy currents are there, which are produced whenever there is a change in magnetic flux. So we conclude that iron bar is a magnet. 15. A stationary charge produces only an electric field around it. When a charge moves with a constant velocity it produces a constant magnetic field in addition to the electric field. As the charge is accelerated, both electric and magnetic fields change with time and space. One becomes the source of the other, thus giving electromagnetic waves. CBSE XII | PHYSICS Sample Paper – 4 Solution 16. Image of the object is formed at focus of objective. This image acts like an object for virtual image of 1 L . Now virtual image produced by 1 L should be located at the focus of 2 . L Since 12 2 /3 L L f ? Image distance from 1 is /3 L v f ?? 1 1 1 f v u ? ? ? 1 3 1 f f u ? ? ? /4 uf ? ? ? 17. (i) Actual depth t =12.5 cm Apparent depth a = 9.4 cm 12.5 1.33 9.4 aw t a ? ? ? ? (ii) 1.63 al ? ? 12.5 7.7 1.63 l al t a cm ? ? ? ? Therefore, the microscope has to be moved by ? ? 9.4 7.7 , cm ? i.e., 1.7 cm 18. The capacitor can be considered as split into two capacitors in series as shown below Here, 1 2 0 12 22 o K A k A c and c dd ?? ?? The capacitance of capacitors in series is 12 1 1 1 c c c ?? 12 12 cc c cc ?? ? 12 12 2 o A kk c d k k ??? ? ?? ? ?? CBSE XII | PHYSICS Sample Paper – 4 Solution OR Let ? be the surface charge density of capacitor plates of area A. Electric field between the plates in the air space is o o E ? ? ? As in case of conducting slab ? po EE net electric field inside the conducting slab is zero. Now potential difference between the plates of capacitor is ? ? ? ? o o V E d t d t ? ? ? ? ? ? QA ? ? 1/ oo AC Q C V d t t d ? ? ? ? ?? Where o o EA C d ? 19. Since 100 ? ? 3 2 10 A ?; ?; ? ? ?? ? ? ? c CE BE BC I V V VRead More

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