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# The amount of electrical current that flows through a wire is inversel

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Math Expert
Joined: 02 Sep 2009
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The amount of electrical current that flows through a wire is inversel [#permalink]

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24 Jun 2015, 00:16
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The amount of electrical current that flows through a wire is inversely proportional to the resistance in that wire. If a wire currently carries 4 amperes of electrical current, but the resistance is then cut to one-third of its original value, how many of electrical current will flow through the wire?

A. 3/4 amperes
B. 4/3 amperes
C. 4 amperes
D. 8 amperes
E. 12 amperes

Kudos for a correct solution.
[Reveal] Spoiler: OA

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Re: The amount of electrical current that flows through a wire is inversel [#permalink]

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24 Jun 2015, 02:06
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Let I1 be the initial current and R1 be the initial resistance.

I1 is inversely proportional to R1
i.e I1 = k/ R1 ; where k is some constant.

From the given data:
4 = k / R1
k = 4R1

Given R2 = R1/3
I2
= k/R2
= k/ R1/3
= 3k/ R1
= 3 * 4* R1/ R1
= 12 A

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Re: The amount of electrical current that flows through a wire is inversel [#permalink]

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24 Jun 2015, 05:43
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The amount of electrical current that flows through a wire is inversely proportional to the resistance in that wire. If a wire currently carries 4 amperes of electrical current, but the resistance is then cut to one-third of its original value, how many of electrical current will flow through the wire?

A. 3/4 amperes
B. 4/3 amperes
C. 4 amperes
D. 8 amperes
E. 12 amperes

Solution:

Given that, I∝1/R

I1=4 amps, I2=?
R2=(1/3)R1

Substitute the values in the equation (I1/I2)=(R2/R1) -> (4/I2) = (R1/3R1)

-> I2 = 12. ANS E.

Thanks

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Re: The amount of electrical current that flows through a wire is inversel [#permalink]

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24 Jun 2015, 06:08
Bunuel wrote:
The amount of electrical current that flows through a wire is inversely proportional to the resistance in that wire. If a wire currently carries 4 amperes of electrical current, but the resistance is then cut to one-third of its original value, how many of electrical current will flow through the wire?

A. 3/4 amperes
B. 4/3 amperes
C. 4 amperes
D. 8 amperes
E. 12 amperes

Kudos for a correct solution.

Current flow = 4 ampere = 1/4 resistance
New Flow = 12 ampere = 1/12 resistance*

New resistance = 1/3 * 1/4 = 1/12

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Joined: 08 Jul 2010
Posts: 2017
Location: India
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The amount of electrical current that flows through a wire is inversel [#permalink]

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24 Jun 2015, 06:46
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Bunuel wrote:
The amount of electrical current that flows through a wire is inversely proportional to the resistance in that wire. If a wire currently carries 4 amperes of electrical current, but the resistance is then cut to one-third of its original value, how many of electrical current will flow through the wire?

A. 3/4 amperes
B. 4/3 amperes
C. 4 amperes
D. 8 amperes
E. 12 amperes

Kudos for a correct solution.

Directly Proportional : The relation when due to increase in one variable, other variable needs to be increased is called a Directly Proportional Relationship e.g. Speed and Distance. "More Distance in same time require more speed and Vise versa"

Inversely Proportional : The relation when due to increase in one variable, other Variable needs to be Decreased is called a Inversely Proportional Relationship e.g. Speed and Time. "More Speed will cover a specific Distance in Less time and Vise versa"

Given: Current is INVERSELY Proportional to Resistance

i.e. Current = (1/Resistance)*Constant [Removal of Proportional sign always comes with a constant]

i.e. $$Current_1 / Current_2 = Resistance_2 / Resistance_1$$

If Initially Resistance = $$R_1$$
Then, $$R_2 = (1/3)*R_1$$
Current after reducing Resistance, $$C_2 = ?$$
Current Before reducing Resistance, $$C_1 = 4$$

$$4 / C_2 = (1/3)*R_1 / R_1$$

i.e. $$C_2 = 4*3 = 12$$ Amperes

[Reveal] Spoiler:
E

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Re: The amount of electrical current that flows through a wire is inversel [#permalink]

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26 Jun 2015, 08:17
Bunuel wrote:
The amount of electrical current that flows through a wire is inversely proportional to the resistance in that wire. If a wire currently carries 4 amperes of electrical current, but the resistance is then cut to one-third of its original value, how many of electrical current will flow through the wire?

A. 3/4 amperes
B. 4/3 amperes
C. 4 amperes
D. 8 amperes
E. 12 amperes

Kudos for a correct solution.

Current * resistance = K constant.

If resistance is dropped to 1/3rd then current must be tripled to maintain the product constant.

Hence Option E is correct.
Math Expert
Joined: 02 Sep 2009
Posts: 44419
The amount of electrical current that flows through a wire is inversel [#permalink]

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29 Jun 2015, 06:18
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Expert's post
Bunuel wrote:
The amount of electrical current that flows through a wire is inversely proportional to the resistance in that wire. If a wire currently carries 4 amperes of electrical current, but the resistance is then cut to one-third of its original value, how many of electrical current will flow through the wire?

A. 3/4 amperes
B. 4/3 amperes
C. 4 amperes
D. 8 amperes
E. 12 amperes

Kudos for a correct solution.

MANHATTAN GMAT OFFICIAL SOLUTION:

While you are not given precise amounts for the “before” or “after” resistance in the wire, you can pick numbers. Using 3 as the original resistance and 1 as the new resistance, you can see that the new electrical current will be 12 amperes:

$$C_1R_1=C_2R_2$$;

$$4*3=C_2*1$$;

$$C_2=12$$.

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Re: The amount of electrical current that flows through a wire is inversel [#permalink]

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13 Nov 2015, 19:29
4 = 1/R or R = 1/4
if resistance is cut to 1/3 of what it was, then the new resistance is 1/4 * 1/3 or 1/12

since we know that the amount of electrical current is indirectly proportional to resistance, then 1 : 1/12 = 12. Thus, E is the answer.
Manager
Joined: 25 May 2016
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The amount of electrical current that flows through a wire is inversel [#permalink]

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09 Dec 2017, 18:26
Voltage = Current * Resistance
Resistance drops to 1/3 of original value, therefore current will increase by 3 times.
4 * 3 = 12 A
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Re: The amount of electrical current that flows through a wire is inversel [#permalink]

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03 Jan 2018, 10:21
$$c=\frac{k}{r}$$
$$4=\frac{k}{r}$$
$$k=4r$$

After cutting resistance

$$c=\frac{k}{\frac{r}{3}}$$
$$c=\frac{3k}{r}$$
$$c=\frac{3*4r}{r}$$
$$c=12$$
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Re: The amount of electrical current that flows through a wire is inversel [#permalink]

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04 Jan 2018, 11:50
Bunuel wrote:
The amount of electrical current that flows through a wire is inversely proportional to the resistance in that wire. If a wire currently carries 4 amperes of electrical current, but the resistance is then cut to one-third of its original value, how many of electrical current will flow through the wire?

A. 3/4 amperes
B. 4/3 amperes
C. 4 amperes
D. 8 amperes
E. 12 amperes

Kudos for a correct solution.

For a conceptual discussion of inverse variation, check this link:
https://www.veritasprep.com/blog/2013/0 ... inversely/
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Re: The amount of electrical current that flows through a wire is inversel   [#permalink] 04 Jan 2018, 11:50
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