Question

please answer this question ?

Class - 10th
Chapter - Electricity

Please don't give me wrong answers ​

Answer 1

Given:-

V = 12v, R = 4ohm, I = 7A

To find:-

Value of R

Solution:-

we know, R' = V/I

Let R' be the total resistance and r be the required resistance.

therefore,

R'

$= \frac{12}{7} v$

Now, we know that resistors are connected in parallel,

therefore,

1/R' = 1/r + 1/R

$\frac{1}{ \frac{12}{7} } = \frac{1}{4} + \frac{1}{r}$

$= > \frac{7}{12} - \frac{1}{4} = \frac{1}{r}$

$= > \frac{7 - 3}{12} = \frac{1}{r}$

$= > \frac{4}{12} = \frac{1}{r}$

$= > \frac{1}{3} = \frac{1}{r}$

therefore, r = 3ohm

Hence, he will need a resistor of 3 ohm.

Answer 2

Question :

A student has two resistors 2Ω and 3Ω. He has to put one of them in place of R₂ as shown in the circuit. The current that he needs in the entire circuit is exactly 7A. Show by calculation which of the two resistors he should choose...

Solution :

We are given that,

• Applied pd = 12V
• R₁ = 4Ω
• Current flow (I) = 7A

❖ Concept :

A] In series connection, current flow in each resistor is same but potential differences across the resistors may be different.

B] In parallel connection, potential difference across each resistor is same but the current flow in resistors may be different.

Let current flow in R₁ be I₁ and current flow in R₂ be I₂.

❒ Current flow in R₁ :

➙ V = I₁ × R₁

➙ 12 = I₁ × 4

➙ I₁ = 12/4

➙ I₁ = 3 A

❒ Current flow in R₂ :

Here total current flow in the entire circuit is 7A which will divide into I₁ and I₂$.$

Therefore we can say that,

➙ I = I₁ + I₂

➙ 7 = 3 + I₂

➙ I₂ = 4 A

Applying ohm's law for R₂, we get

➙ V = I₂ × R₂

➙ 12 = 4 × R₂

➙ R₂ = 12/4

➙ R₂ = 3Ω (Final Answer)