Apply Ohm's law to circuits
Scenario
Aapke paas ek `12 V` ki battery aur ek chhota bulb hai, par aap dar rahe ho ki kahin bulb fuse na ho jaye.
Kaise pata chalega ki bulb mein kitna current jayega?
Mental model
Formula `V = IR` ek electrical scale ki tarah hai. Koi bhi do values batao, teesri apne aap mil jayegi.
Agar `V = IR` hai, toh hum easily `I = V / R` aur `R = V / I` nikal sakte hain. Ye triangle (`V` at top, `I` and `R` at bottom) circuit ke kisi bhi component ka behaviour predict karne mein madad karta hai.
Explanation
Circuits solve karte waqt, `V = IR` sabse important tool hai. Is formula ko 'Ohm's magic triangle' ki madad se bhi yaad rakha jata hai.
Agar humein current nikalna hai, toh `I = V / R` use karte hain. Isse saaf pata chalta hai ki current resistance ke inversely proportional hai. Agar resistance double ho jaye, toh current aadha (half) ho jayega.
Agar resistance nikalna ho, toh `R = V / I` use karte hain. Resistance ki unit `Ohm` hai, jise Greek letter `Omega` se dikhate hain. `1 Ohm` wahi resistance hai jab `1 Volt` ki battery `1 Ampere` ka current produce kare.
Hamesha yaad rakho, numerical solve karne se pehle values ko standard units (`Volt`, `Ampere`, `Ohm`) mein convert karna zaroori hai. Milliampere (`mA`) ko `1000` se divide karke `Ampere` mein convert karna na bhoolein.
Worked example
Problem: How much current will an electric bulb draw from a `220 V` source, if the resistance of the bulb filament is `1200 ohm`?
- Question mein di gayi values ko list karte hain.
- Ohm's law formula `I = V / R` use karte hain.
- Divide karke current (`A`) nikalte hain.
Answer: `0.18 A`
Problem: The potential difference between the terminals of an electric heater is `60 V` when it draws a current of `4 A`. What current will the heater draw if the potential difference is increased to `120 V`?
- Pehle case se heater ka resistance `R` nikalte hain, jo ki fix rehta hai.
- Naye voltage ke saath naya current `I` nikalne ke liye formula lagate hain.
- `I = V / R` apply karte hain.
Answer: `8 A`
Key points
- Calculating Current: Use `I = V / R`.
- Calculating Resistance: Use `R = V / I`.
Common mistakes
- Forgetting to convert units: Using current in milliamperes (`mA`) directly in the formula `V = IR`. Always convert `mA` to `A` (`1 mA = 0.001 A`).
Recall questions
- If voltage is doubled while resistance is kept constant, what happens to the current?
- What happens to the current if the resistance is doubled and voltage is constant?
- What does a straight line on a `V-I` graph indicate?
Questions & answers
Let the resistance of an electrical component remains constant while the potential difference across its ends decreases to half of its former value. What change will occur in the current?
The current will also decrease to half of its former value.
Approach: Use the direct proportionality between `V` and `I`.
Find the current if a `12 V` battery is connected to a `6 Ω` resistor.
`2 A`
Approach: `I = V / R = 12 / 6 = 2 A`.
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