Electricity

Electricity and Magnetism Level 2

The electricity line in Richard's study room transports 11 amperes at a voltage difference of the electricity line 220 volt when he has two bulbs in the parallel connection.

What is the value of total resistance of the combination of the electric bulbs in Richard's room (in ohm)?

The answer is 20.

1 solution

Munem Shahriar
May 7, 2017

Electrical current, $I = 11$ $amp$

Voltage difference, $V = 220$ $V$

If the resistance of the bulb is $R$ ,

$V = IR$

$\Rightarrow$ $R =$ $\dfrac{V}{I}$ = $\dfrac{220V}{11 amp}$

Therefore $R = 20$ $ohm$

If the total resistance is 20, each bulb therefore has a resistance of 40, since they are in parallel. It sounds like the answer should be 40, since it is asking for the bulb resistance.

Steven Chase - 4 years, 1 month ago

Please write the whole solution where the answer is 40 . In my solution i used V= IR . Value of R = $\frac{220V}{11 amp}$ and got the answer of 20. I see nothing wrong here.

Munem Shahriar - 4 years, 1 month ago

That's the total effective resistance. Since you've got two bulbs in parallel, each one will have a resistance of 40 if the total is 20. In general, if two identical resistors are in parallel, the effective resistance of the pair will be half the resistance of each.

Steven Chase - 4 years, 1 month ago

I also think Steven is right, even I entered 40 as my initial answer.

Ananya Agrahari - 3 years, 10 months ago

@Ananya Agrahari – Do you mean one electric bulb resistance is 20 and two electric bulb resistance is 40?

Munem Shahriar - 3 years, 10 months ago

@Munem Shahriar – No I mean that Resistance of each bulb is 40 but as they are connected in parallel so equivalent must be 20 , not individual resistance is 20.

Ananya Agrahari - 3 years, 10 months ago

@Ananya Agrahari – But by the resistance formula, I got the answer of 20. Can you show me your working for answer 40?

Munem Shahriar - 3 years, 10 months ago

@Munem Shahriar – There are 2 resistors connected in parallel right? Using V=IR you get equivalent resistance 20 ohms. For resistors connected in parallel formula is 1/R=(1/R1)+(1/R2). here resistance should be consider equal therefore, 1/R=(2/R1) as R1 and R2 are considered of same resistance and R is equivalent resistance i.e 20 now 1/20=(2/R1) therefore R=40 ohms.

Ananya Agrahari - 3 years, 10 months ago

@Ananya Agrahari – Thanks for the information. Can you report this problem? then staffs could update the answer to 40.

Munem Shahriar - 3 years, 10 months ago

@Munem Shahriar – Okay, sure

Ananya Agrahari - 3 years, 10 months ago

Electricity

The answer is 20.

1 solution

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