Assignment 2a Solutions
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Name: ______________________________Student no: _____________ Group:_______________ CC2404 Applied Physics and Instrumentation in Health Care Assignment 2a (2009) 1.
When a stimulus applied to a nerve cell, the cell is said depolarized. Which ion rushes into the inside cell. a. K+ b. Clc. Na+ d. K+ and ClAnswer____c_____
2.
For main commercial supply frequencies (50-60 Hz), the can’t let go current is about: a. 1 mA b. 5 mA c. 15 mA d. 100 mA Answer____C____
3.
(1 mark)
(1 mark)
Which of the following has the correct meaning for a typical ECG waveform? a. P-wave : depolarization of ventricles b. QRS-wave: depolarization of ventricles c. P-wave : re-polarization of ventricles d. T-wave: depolarization of atria Answer____b____
(1 mark)
4. A platinum wire 80cm long is to have a resistance of 0.1 Ω . What should its diameter be? The resistivity of platinum is 1.1 x 10-7 Ω ‧m. Solution: R = ρ
−7 L L = ρ 2 , ∴r = ρL = 1.1x10 x 0.8 = 5.3 x10 −4 m A πr πR πx 0.1
the diameter should be 1.06x10-3m or 1.06mm
(2 marks) (1 marks)
5. A 120 W light bulb is designed to operate on 220 V AC. (a)What is the rms current drawn by the bulb? (b)What is the peak current? (c) What is the resistance of the bulb’s filament? Pav 120 = = 0.545 A Solution: (a) I rms = Vrms 220 (b) I o = 2 I rms = 2 × 0.545 = 0.77 A (c) R =
Vrms 220 V 2 rms 2202 = = 404 Ω or R = = = 404Ω I rms 0.545 Pav 120
(1 mark) (1 mark) (1 mark)
Name: ______________________________Student no: _____________ Group:_______________ 6. A negative hydrogen ion has an extra electron and a mass of 1.67 ×10 −27 kg . (a) Calculate its kinetic energy at 1.0% of speed of light (c= 3 ×10 8 m / s ) . (b) What acceleration voltage is needed −19 to obtain this energy? ( q e = −1.6 ×10 C )
Solution: a. K =
1 1 mv 2 = ×1.67 ×10 −27 × (0.01 × 3 ×10 8 ) 2 = 7.52 ×10 −15 J 2 2
(2 marks)
b. this kinetic energy is transformed by an electrical potential energy change ∆ EPE = QV, therefore : V =
∆EPE 7.52 ×10 −15 = = −46969 V = −46 .97 kV Q − 1.6 ×10 −19
(2 marks)
When a stimulus applied to a nerve cell, the cell is said depolarized. Which ion rushes into the inside cell. a. K+ b. Clc. Na+ d. K+ and ClAnswer____c_____
2.
For main commercial supply frequencies (50-60 Hz), the can’t let go current is about: a. 1 mA b. 5 mA c. 15 mA d. 100 mA Answer____C____
3.
(1 mark)
(1 mark)
Which of the following has the correct meaning for a typical ECG waveform? a. P-wave : depolarization of ventricles b. QRS-wave: depolarization of ventricles c. P-wave : re-polarization of ventricles d. T-wave: depolarization of atria Answer____b____
(1 mark)
4. A platinum wire 80cm long is to have a resistance of 0.1 Ω . What should its diameter be? The resistivity of platinum is 1.1 x 10-7 Ω ‧m. Solution: R = ρ
−7 L L = ρ 2 , ∴r = ρL = 1.1x10 x 0.8 = 5.3 x10 −4 m A πr πR πx 0.1
the diameter should be 1.06x10-3m or 1.06mm
(2 marks) (1 marks)
5. A 120 W light bulb is designed to operate on 220 V AC. (a)What is the rms current drawn by the bulb? (b)What is the peak current? (c) What is the resistance of the bulb’s filament? Pav 120 = = 0.545 A Solution: (a) I rms = Vrms 220 (b) I o = 2 I rms = 2 × 0.545 = 0.77 A (c) R =
Vrms 220 V 2 rms 2202 = = 404 Ω or R = = = 404Ω I rms 0.545 Pav 120
(1 mark) (1 mark) (1 mark)
Name: ______________________________Student no: _____________ Group:_______________ 6. A negative hydrogen ion has an extra electron and a mass of 1.67 ×10 −27 kg . (a) Calculate its kinetic energy at 1.0% of speed of light (c= 3 ×10 8 m / s ) . (b) What acceleration voltage is needed −19 to obtain this energy? ( q e = −1.6 ×10 C )
Solution: a. K =
1 1 mv 2 = ×1.67 ×10 −27 × (0.01 × 3 ×10 8 ) 2 = 7.52 ×10 −15 J 2 2
(2 marks)
b. this kinetic energy is transformed by an electrical potential energy change ∆ EPE = QV, therefore : V =
∆EPE 7.52 ×10 −15 = = −46969 V = −46 .97 kV Q − 1.6 ×10 −19
(2 marks)
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