W3b_Lab_Quizzes_3_attempts_3LB_Basic_Physics_Lab_II

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Apr 3, 2024

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W3b: Lab Quizzes (3 attempts) Due Jan 26 at 11:59pm Points 5 Questions 4 Available after Jan 21 at 11:59pm Time Limit None Allowed Attempts 3 Instructions Attempt History Attempt Time Score LATEST Attempt 1 6 minutes 5 out of 5 Score for this attempt: 5 out of 5 Submitted Jan 22 at 11:41am This attempt took 6 minutes. The weekly lab quiz is due Friday midnight of the respective week. However, as much as possible, you should try to do the quiz before your lab section. You definitely need to read and understand the materials before the beginning of your section; otherwise you risk not being able to finish your lab exercises which will lead to a lower lab report score. If you have questions about grading or mistakes in the quiz, contact your Instructor and/or TAs. NOTE: In this Quiz, you will have THREE Attempts. Take the Quiz Again 1 / 1 pts Question 1

Answer 1: Answer 2: DC versus AC problem. Suppose your DC power supply is set to 15 V and the vertical setting on the oscilloscope is at 5 V/div. How many divisions will the trace deflect if you connect the output of the power supply to the scope with the "A input" switch set on DC? How many divisions if the switch is on AC? Please write your answer with integer values. 3 divisions for DC, 0 divisions for AC, 3 Correct! Correct! 0 Correct! Correct! 1 / 1 pts Question 2

Maximum current problem. If the current on your power supply exceeds 500 mA it can damage the supply. Suppose the supply is set for 37 V. What is the smallest resistance you can measure? Please round your answer to the nearest integer. ________________ Ω ; 74 Correct! Correct! orrect Answers orrect Answers 74 1 / 1 pts Question 3

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Internal resistance problem. Suppose that in Figure 3.3, V =5V, R =150k Ω , R =450k Ω , and R =1.4M Ω . Initially, the voltmeter is disconnected. EXAMPLES: What is the voltage across R ? [Answer: 3.75 V.] What is the voltage across R with the meter connected? [Answer: 3.47107438016529 V.] QUESTION: If the internal resistance of the meter were 15 M Ω , what is the voltage across R ? Please write your answer with two decimal places. ___________________Volts For help finding the equivalent resistance, click here. (http://physics.bu.edu/py106/notes/Circuits.html) o 1 2 i 2 2 2 3.72 Correct! Correct! orrect Answers orrect Answers 3.7221 (with margin: 0.01)

2 / 2 pts Question 4 PHYSIOLOGY OF SHOCKS; ELECTROSURGERY READING 1 The magnitude of the current that flows through the body from an external source is determined by Ohm's law and therefore depends on the applied voltage and the resistance of the body. For DC and low frequency (household) voltages, the resistance of the skin at the contact location limits the current (at higher frequencies, the internal body resistance is most important). Therefore, in household conditions, the amount of current that will flow through the body depends upon the condition of the skin at the contact location. Dry skin has a resistance as high as 10 Ω but only 1 % of this value if it is wet (the total resistance of the body between normal, perspiring hands is 1500 Ω ). 5

If you grab a "live" wire that passes about 25 mA through your hand, you probably will not be able to release the wire (7). The wire does not capture your hand with an electrical force. Instead, the current through the hand muscles causes the hand muscles to contract, clamping your hand around the wire. Electricians working with live or potentially live wires often use the back of their hands or fingers to move the wires. If the touch does draw current, the muscle contraction then throws the hand away from the wire (7). (7) Jearl Walker, THE FLYING CIRCUS OF PHYSICS WITH ANSWERS, (New York, John Wiley & Sons, 1977). Assume that a particular person's skin is found to have a resistance of 1 x 10 Ω when dry and 1400 Ω when wet. How much current will flow into the body on contact with a 120 V household AC outlet with wet and dry skin. Please round your answers to one decimal place. 1.2 mA (dry skin) 85.7 mA (wet skin) 5

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