PHY104 Pre Lab Problems: Joule Heating Problem #1: A five volt heating element (

Question

PHY104 Pre Lab Problems: Joule Heating Problem #1: A five volt heating element (E = 5V) draws one ampere of current (I = 1 A) for five minutes. (a) Find the electrical power input, (b) sketch the power versus time (in seconds) graph for 300s, (c) find the electrical energy input produced in five minutes and (d) sketch the energy versus time graph for zero to 300s. Include values on each axis. Ans: (a) 5 W, (c) 1500 J Problem #2: If the heater of Problem #1 is immersed in 200g of water in a 50g aluminum calorimeter what is the final temperature of the water if it starts out at 25 degree C? Hint: Ignore any heat loss due to conduction. Solve the Input/ Output Energy Conversion equation (less the heat loss term, H triangle T) of P. 3-3 for triangle T or (Tf - Ti) as shown below, then find the final temperature, Tf = 25 degree + triangle T. Ans: 26.7 degree C

Explanation / Answer

(a) Electric power = energy / time

= V I t / t

= V I

= 5V * 1A

= 5 W

(d) Electric energy = power * time

= V I t

= 5V * 1A* (5 * 60s)

= 1500 J

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