Physics Exam Answers: Spring Semester 2004-5
Level One
F31SA1: Introduction to Astronomy
2. (a) K = 1 ; (b) v = 13,000 m s-1.
3. (c) t = 1.5 1014 years ; this is >> age of universe (1.5 1010 years).
4. (c) L = 2000 L๏
6. (d) M = 6.5 ; (e) D = 5000 pc.
7. (d) M = 1.9 1011 M๏ ; (f) M = 1010 M๏ .
8. (c) Emax = 1.9 ; (d) RES = 0.02 arc sec. ; (e) max = 21º .
F31SE1: Radio and Communications
1. Minimum frequency = 23.7 MHz.
2. Minimum transmitter power = 0.36 mW.
3. Bandwidth needed = 24 KHz.
5. Reference Oscillator Freq. = 0.1 MHz ; D = 880 to 1080.
6. Proportion of total power in sidebands = 1/9 .
7. Max. length = 1500 m. ; Max.length for single mode fibre = 10,000 m.
8. VSWR = 1.5 ; Power = 9.6 W ; R = 33 ; 4 repeaters needed.
F31SM3: Vibrations and Waves
1. (b) = 10 rad s-1 ;
2. (b) d = 5.45 cm.
3. (a) = 1 m. ; (b) = 20 rad s-1 ; (c) v = 10 ms-1 ; (d) = 0.05 Kg m-1 .
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, F31SQ1: Space-Time and Matter
1. Ratio = 0.92 .
2. v = 2.846 108 ms-1 .
3. No. of photons per sec. = 3.01 1016 ; Kinetic energy = 4.18 eV.
4. P 5.28 10-21 kg m s-1 ; K > 52.0 keV.
5. d = 2.5 10-10 m.
( v A vB )
6. (a) Earth recession speed = -vA ; (b) B recession speed = .
1 v AvB / c 2
According to Earth observer, LA = 47.7 m. and LB = 45.8 m. According to
Rocket B observer, LA = 39.03 m.
7. p = 3.5 10-18 Ns ; v = 2.6 108 ms-1 .
8. Photon freq. emitted : 31 = 2.921 1015 Hz ; 32 = 4.5641 1014 Hz ; 31 =
2.46 1015 Hz ; No. of photons needed = 840.
F31ST1: Thermal and Kinetic
2. 10 ways of arranging quanta; i.e. one oscillator has 3 and the others none
(total 3); one oscillator has 2, one has 1 and the other zero (total 6); an equal
sharing among the three oscillators (total 1).
4. Best efficiency is given by 1-(TL/TH) = 75%; so engineer's claim not valid.
α 2
Work done = P0 (V2 V1 ) (V2 V1 ) .
2
5.
2
6. AB: Q = +3740 J ; W = 0 ; U = +3740 J.
BC: Q = 0 ; W = -1876 J ; U = -1876 J.
CA: Q = -3220 J ; W = 1111J ; U = -1901 J.
3
m 2 4
7. (b) A = .
2kT
8. (b) (iii) and (iv) are possible answers;
(c) Total change (single stage) = +0.04C JK-1 ; Total change (two stage) = +0.04C JK-1
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Level One
F31SA1: Introduction to Astronomy
2. (a) K = 1 ; (b) v = 13,000 m s-1.
3. (c) t = 1.5 1014 years ; this is >> age of universe (1.5 1010 years).
4. (c) L = 2000 L๏
6. (d) M = 6.5 ; (e) D = 5000 pc.
7. (d) M = 1.9 1011 M๏ ; (f) M = 1010 M๏ .
8. (c) Emax = 1.9 ; (d) RES = 0.02 arc sec. ; (e) max = 21º .
F31SE1: Radio and Communications
1. Minimum frequency = 23.7 MHz.
2. Minimum transmitter power = 0.36 mW.
3. Bandwidth needed = 24 KHz.
5. Reference Oscillator Freq. = 0.1 MHz ; D = 880 to 1080.
6. Proportion of total power in sidebands = 1/9 .
7. Max. length = 1500 m. ; Max.length for single mode fibre = 10,000 m.
8. VSWR = 1.5 ; Power = 9.6 W ; R = 33 ; 4 repeaters needed.
F31SM3: Vibrations and Waves
1. (b) = 10 rad s-1 ;
2. (b) d = 5.45 cm.
3. (a) = 1 m. ; (b) = 20 rad s-1 ; (c) v = 10 ms-1 ; (d) = 0.05 Kg m-1 .
44
, F31SQ1: Space-Time and Matter
1. Ratio = 0.92 .
2. v = 2.846 108 ms-1 .
3. No. of photons per sec. = 3.01 1016 ; Kinetic energy = 4.18 eV.
4. P 5.28 10-21 kg m s-1 ; K > 52.0 keV.
5. d = 2.5 10-10 m.
( v A vB )
6. (a) Earth recession speed = -vA ; (b) B recession speed = .
1 v AvB / c 2
According to Earth observer, LA = 47.7 m. and LB = 45.8 m. According to
Rocket B observer, LA = 39.03 m.
7. p = 3.5 10-18 Ns ; v = 2.6 108 ms-1 .
8. Photon freq. emitted : 31 = 2.921 1015 Hz ; 32 = 4.5641 1014 Hz ; 31 =
2.46 1015 Hz ; No. of photons needed = 840.
F31ST1: Thermal and Kinetic
2. 10 ways of arranging quanta; i.e. one oscillator has 3 and the others none
(total 3); one oscillator has 2, one has 1 and the other zero (total 6); an equal
sharing among the three oscillators (total 1).
4. Best efficiency is given by 1-(TL/TH) = 75%; so engineer's claim not valid.
α 2
Work done = P0 (V2 V1 ) (V2 V1 ) .
2
5.
2
6. AB: Q = +3740 J ; W = 0 ; U = +3740 J.
BC: Q = 0 ; W = -1876 J ; U = -1876 J.
CA: Q = -3220 J ; W = 1111J ; U = -1901 J.
3
m 2 4
7. (b) A = .
2kT
8. (b) (iii) and (iv) are possible answers;
(c) Total change (single stage) = +0.04C JK-1 ; Total change (two stage) = +0.04C JK-1
45
