2068 Integrated Concepts a What is the cost of heating a hot tub containing

# 2068 integrated concepts a what is the cost of

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(20.68) Integrated Concepts (a) What is the cost of heating a hot tub containing 1500 kg of water from C 0 . 10 to C 0 . 40 , assuming 75.0% efficiency to account for heat transfer to the surroundings? The cost of electricity is 12 cents/kW h . (b) What current was used by the 220-V AC electric heater, if this took 4.00 h?
OpenStax College Physics Chapter 18-21 Solution (a) 28 . 6 \$ h kW 1 0900 . 0 \$ J 10 60 . 3 kWh 1 J) 10 51 . 2 ( Cost J 10 51 . 2 750 . 0 ) C 0 . 30 )( C J/kg 4186 )( kg 1500 ( 750 . 0 6 8 8 w T mc Q (b) t Q IV P , where s 400 , 14 h 00 . 4 t , so that A 2 . 79 ) s 400 , 14 )( V 220 ( J 10 51 . 2 8 Vt Q I 7. (21.38) Find the currents flowing in the circuit in Figure 21.52 . Explicitly show how you follow the stepsc in the Problem-Solving Strategies for Series and Parallel Resistors . Solution First, simplify the circuit by adding up resistors in series: 25 . 78 20 . 0 05 . 0 78 and , 5 . 40 40 50 . 0 , 1 . 25 20 10 . 0 0 . 5 4 3 3 s3 2 2 s2 5 1 1 s1 r r R R R r R R r R R Applying the junction rule to point a and the loop rule to loops abcdelka and aklefghija yields: 3 2 1 I I I (i) 0 5 . 40 1 . 25 V 0 . 24 or , 0 2 1 s2 2 s1 1 2 1 I I R I R I E E (ii)
OpenStax College Physics Chapter 18-21 0 25 . 78 5 . 40 V 0 . 18 or , 0 3 2 s3 3 s2 2 4 3 2 I I R I R I E E E (iii) First solve Equation (ii) for 3 I (omitting units): 956 . 0 614 . 1 2 1 I I (iv) Now solve Equation (iii) for 3 I : I I 518 . 0 230 . 0 3 (v) Substitute (iv) and (v) into (i): A 0.379 A 0.3787 so , 956 . 0 1.614 518 . 0 230 . 0 2 2 2 1 3 2 I I I I I I Substituting this value for 2 I into (iv) gives:  A 345 . 0 or , 956 . 0 3787 . 0 614 . 1 1 1 I I Substituting the value for 2 I into (v) gives: A 034 . 0 or , 3787 . 0 518 . 0 230 . 0 3 3 I I 8. (21.50) Suppose you measure the terminal voltage of a 1.585-V alkaline cell having an internal resistance of 100 . 0 by placing a k - 00 . 1 voltmeter across its terminals. ( Figure 21.54 .) (a) What current flows? (b) Find the terminal voltage. (c) To see how close the measured terminal voltage is to the emf, calculate their ratio.

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• Fall '18
• Afrifa
• Electric charge, OpenStax College Physics

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