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Exercises - Problems - Electricity - Electrodynamics

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1) A student wants to plug a small lamp (with an operating voltage of 4,5V and operating power of 2.25W) in a 12V battery, according to the circuit shown. The resistance needed in this circuit is:

 

a) 0,5 Ω b) 4,5 Ω c) 9,0 Ωd) 12 Ωe) 15 Ω


 

 

2) Six batteries, each with a voltage V, are connected in parallel , as shown on the image, to a gadget with resistance R. The current read in the amperimeter A is:

a) V/ R b) 2V/ R c) 2V/ 3R d) 3V/ R e) 6V/ R

 


3) A kitchen electric circuit is shown below, where A and B are electric outlets and D is a circuit breaker. It is necessary that a microwaves oven and a dishwasher are simultaneously plugged on these outlets. For this to happen safely, the circuit breaker must be of at least:

dishwasher: 110 V, 1400 W

microwaves oven: 110V , 920 W

 

a) 10 A b) 15 A c) 20 A d) 25 A e) 30 A


4) Electrical energy generated at the Itaipu power plant in Brazil travels to São PAulo (900 km away) in a transmission line, at a 750 kV voltage. If the urban transmission line voltage (which is 30 kV) was used , what would be the power loss (via Joule effect)?

 

 

a) 27.000 times larger b) 625 times larger c) 30 times larger d) 25 times larger e ) the same

 

 

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