To Verify Laws of Parallel Resistances (Class 10 Physics Practical)
To verify the laws of parallel resistances and demonstrate that reciprocal of total resistance equals sum of reciprocals of individual resistances
TL;DR: To verify the laws of parallel resistances and demonstrate that reciprocal of total resistance equals sum of reciprocals of individual resistances
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Aim: To verify the laws of parallel resistances and demonstrate that reciprocal of total resistance equals sum of reciprocals of individual resistances
Materials Required
- Three resistors of known values
- Ammeter
- Voltmeter
- Rheostat
- Battery and switch
- Connecting wires
- Plugged key
Theory
In parallel circuits, resistors are connected across same voltage source so voltage across each is same. Current divides among resistors inversely proportional to their resistance. The reciprocal law states: 1/R_total = 1/R1 + 1/R2 + 1/R3. Parallel arrangement is used when same voltage is needed across multiple devices.
Procedure
- Connect three resistors in parallel between battery terminals
- Connect ammeter in series with battery to measure total current
- Connect voltmeter across parallel combination
- Close switch and note voltmeter reading
- Insert ammeter in series with first resistor and note current I1
- Similarly measure currents I2 and I3 through second and third resistors
- Measure total current I_total from battery
- Calculate resistances using R = V/I
- Verify reciprocal law: 1/R_total = 1/R1 + 1/R2 + 1/R3
Observation
Voltage remains same across all resistors. Different currents flow through different resistors based on their resistance. Total current: I_total = I1 + I2 + I3. Smaller resistance carries larger current. Total current is sum of individual currents.
Result
Law of parallel resistances verified: 1/R_total = 1/R1 + 1/R2 + 1/R3. Total resistance less than smallest individual resistance. Current distribution verified.
Precautions
- Use suitable ammeter range for measuring currents
- Ensure voltmeter reads same value across all parallel branches
- Connect ammeter in series with each branch separately
- Start with maximum rheostat resistance
- Avoid short circuits while changing connections
Viva Questions
What is parallel connection of resistors?
Parallel connection is when multiple resistors are connected across same voltage source with different current paths.
How do currents behave in parallel circuit?
In parallel circuit, total current equals sum of individual currents through each branch: I_total = I1 + I2 + I3.
What is the reciprocal law for parallel resistance?
The reciprocal law states that 1/R_total = 1/R1 + 1/R2 + 1/R3. The reciprocal of equivalent resistance equals sum of reciprocals.
Why is current distribution unequal in parallel circuit?
In parallel circuit, current is inversely proportional to resistance. Lower resistance branches draw more current while higher resistance draws less.
What happens if one resistor burns out in parallel circuit?
If one resistor burns out in parallel circuit, only that branch breaks. Other branches continue to work as they have separate paths.
Which connection needs lower voltage source: series or parallel?
Parallel connection needs lower voltage source compared to series because same voltage appears across each resistor in parallel arrangement.
More Class 10 Physics Practicals
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