If one has a certain current in an electric circuit and for some reason wishes t

Question

If one has a certain current in an electric circuit and for some reason wishes to decrease this current to one-third its original value, how could this be done? What current will exist in a resistance of 25 ohms if 125 volts are applied across the resistor? Are the following statements true or false: The resistance of a wire varies inversely as its length. The resistance of a wire varies directly as its cross-sectional area. If wire of very small cross-sectional area is used to connect the lights in your house, what two undesirable effects will result? In some manner (such as discussing the matter with an electrician) find out what size wire is most commonly used in house wiring. What is the diameter of this wire? Find this diameter in a wire table. Is the resistance of 100 meters of aluminum wire the same as the resistance of 100 meters of copper wire of the same cross-sectional area? If not, is it more or less? A certain wire has a resistance of 60 ohms. If a wire made of the same metal but of 3 times the length and 4 times the cross-sectional area is used in its place, what is the new resistance?

Explanation / Answer

1)

here by using ohms law

I = V / R

we want to decrease the current to 1/3

then the resistance is increase by 3times

1/3 = V/3*R

then the current will deacrese to 1/3 of its orignal value

2)

I = V / R

I = 125 / 25

I = 5 amp

3)

R = rho * L / A

the resistance is directly proportional to resistivity and length of the wire

and inversely proportional to the cross sectional area

therefore both the statements given are wrong

4)

here is also the same concept

R = rho * L / A

the resistance is inversely proportional to the cross sectional area

so if the area is small the resistance will be larger

or if the resistance is large the more current will pass

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