{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

HW5solutions-10

# HW5solutions-10 - Physics 2213 HW#5 Solutions Spring 2010...

This preview shows pages 1–3. Sign up to view the full content.

Physics 2213 HW #5 – Solutions Spring 2010 26.23. [Kirchoff’s Circuit Rules] We have to use Kirchoff’s rules to find the unknown currents, emfs, and resistances. Apply the junction rule at points a, b, c and d to calculate the unknown currents. Then apply the loop rule to three loops to calculate 1 2 , and . R ε ε The circuit is sketched to the right. (a) Apply the junction rule to point a : 3 3.00 A 5.00 A 0 I + = 3 8.00 A I = Apply the junction rule to point b : 4 2.00 A 3.00 A 0 I + = 4 1.00 A I = Apply the junction rule to point c : 3 4 5 0 I I I = 5 3 4 8.00 A 1.00 A 7.00 A I I I = = = As a check, apply the junction rule to point d : 5 2.00 A 5.00 A 0 I = 5 7.00 A I = (b) Apply the loop rule to loop(1): ( )( ) ( ) 1 3 3.00 A 4.00 3.00 0 I ε Ω − Ω = ( )( ) 1 12.0 V 8.00 A 3.00 36.0 V ε = + Ω = Apply the loop rule to loop (2): ( )( ) ( ) 2 3 5.00 A 6.00 3.00 0 I ε Ω − Ω = ( )( ) 2 30.0 V 8.00 A 3.00 54.0 V ε = + Ω = (c) Apply the loop rule to loop (3): ( ) 1 2 2.00 A 0 R ε ε + = 2 1 54.0 V 36.0 V 9.00 2.00 A 2.00 A R ε ε = = = Finally, we can apply the loop rule to loop (4) as a check of our calculations: ( ) ( )( ) ( )( ) 2.00 A 3.00 A 4.00 5.00 A 6.00 0 R Ω + Ω = ( )( ) 2.00 A 9.00 12.0 V 30.0 V 0 Ω − + = 18.0 V 18.0 V 0 + = 26.50. [Electric Dryer] (a) VI P = , so I = P V = 4100 W 240 V = 17.1 A. Recall from page 201 that 12-gauge wire can carry up to 20A safely. Thus, we can use 12-gauge wire safely for this electric dryer. (b) 2 V P VI R = = . Solving for the resistance, R = V 2 P = (240 V) 2 4100 W = 14 . (c) At 11 / c per kWH, for 1 hour the cost is (11 / c/kWh)(1 h)(4.1 kW) = 45 / c . (d) It makes sense that the cost to operate the device is proportional to its power consumption. The number also sounds about right. I am charged about one dollar to run a load of clothes through a dryer for an hour.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document