Each of the four circuits contains three, 10 Ohm, resistors. Which of the four c

Question

Each of the four circuits contains three, 10 Ohm, resistors. Which of the four combinations shown above produces the least total resistance? a) A b) B c) C d) D The energy required to operate a 100 W lamp, 5 hours a day for 30 days is a) 1.5 kW hr b) 15 kW hr c) 150 kW hr d) 1500 kW hr e) 150000 kW h The total equivalent resistance between points X and Y in the circuit shown above is a) 3 Ohm b) 4 Ohm c) 5 Ohm d) 6 Ohm e) 7 Ohm How do the currents I_1, I_2, and I_3 compare? a) I_1 > I_2 > I_3 b) I_1 > I_3 > I_2 c) I_2 > I_1 > I_3 d) I_3 > I_1 > I_2 e) I_3 > I_2 > I_1

Explanation / Answer

14 ans

A=>the equivalent resistance Req=10+10+10=30 ohms

B=>the equivalent resistance Req=10+{10*10/10+10}=15 ohms

C=>the equivalent resistance Req=10*10*10/10+10+10=33.3 ohm

D=>the equivalent resistance Req=20*10/20+10=6.7 ohm

the correct option is d

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15 ans

Given that

power P=100 w

time t=30*5=150 hours

now we find the energy

energy E=100*150=15000 W.hr

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16 ans

2 ohm and 2 ohm are parallel connection

resistance R=2*2/4=1 ohm

resistance R and 2 ohm are series connection

the equivalent resistance Req=2+1=3 ohm

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17 ans

2000 ohm and 6000 ohms are parallel connection

resistance R=2000*6000/8000=1500 ohm

the resistance R and 2500 are series connection

the equivalent resistance Req=2500+1500=4000 ohm

now we find the current I1

current I1=12/4000=3*10^-3 A

now we find the current at 2000 ohms

current I2=2000*3*10^-3/2000+6000=0.75*10^-3 A

now we find the current at 6000 ohms

current I3=6000*3*10^-3/8000=2.25*10^-3 A

the current rank I2>I3>I1

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