SPM Physics Amali: Resistance Depends on Material

 

Constantant swg 28 vs Nichrome swg 28 vs Cooper swg 28

Nichrome, a non-magnetic 80/20 alloy of nickel and chromium, is the most common resistance wire for heating purposes because it has a high resistivity and resistance to oxidation at high temperatures.

🧵 Does the Type of Wire Affect Resistance?

Rintangan dawai bergantung pada jenis bahan yang digunakan. Bahan yang berbeza mempunyai kerintangan tentu (ρ) yang berbeza.

The resistance of a wire depends on the material used. Different materials have different resistivities (ρ).

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👀 Key Observations | Pemerhatian Penting

✅ Semua dawai mempunyai saiz yang hampir sama (SWG 28).

✅ All wires have approximately the same diameter (SWG 28).

✅ Panjang dawai yang digunakan adalah sama.

✅ The wires used have the same length.

✅ Bacaan arus berbeza apabila bahan dawai ditukar.

✅ The current reading changes when the wire material is changed.

✅ Ini menunjukkan setiap bahan mempunyai rintangan yang berbeza.

✅ This shows that different materials have different resistance values.

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❌ Common Mistakes

❌ Menganggap semua dawai mempunyai rintangan yang sama.

❌ Assuming all wires have the same resistance.

❌ Mengelirukan rintangan (R) dengan kerintangan tentu (ρ).

❌ Confusing resistance (R) with resistivity (ρ).

❌ Tidak mengawal panjang dan diameter dawai semasa membuat perbandingan.

❌ Failing to keep wire length and diameter constant during comparison.

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⚠️ Safety / Handling

⚠️ Matikan bekalan kuasa selepas mengambil bacaan.

⚠️ Switch off the power supply after taking readings.

⚠️ Dawai rintangan boleh menjadi panas apabila arus mengalir terlalu lama.

⚠️ Resistance wires may become hot if current flows for a long period.

⚠️ Elakkan menyentuh bahagian dawai yang panas.

⚠️ Avoid touching heated sections of the wire.

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🎯 SPM Exam Tip

📌 Untuk dawai yang mempunyai panjang dan diameter yang sama:

📌 For wires with the same length and diameter:

Copper → Lowest Resistance

Constantan → Higher Resistance

Nichrome → Highest Resistance

📌 Tembaga membenarkan arus mengalir dengan lebih mudah.

📌 Copper allows current to flow more easily.

📌 Nichrome mempunyai kerintangan tentu yang tinggi.

📌 Nichrome has a high resistivity.

📌 Sebab itu nichrome digunakan dalam elemen pemanas.

📌 That is why nichrome is commonly used in heating elements.

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🧠 SPM Concept Check

Formula yang perlu diingati:

Formula to remember:

R = ρL/A

di mana / where:

• R = Resistance
• ρ = Resistivity
• L = Length of wire
• A = Cross-sectional area

📌 Jika panjang dan diameter adalah tetap, rintangan bergantung kepada nilai ρ (resistivity).

📌 If length and diameter are fixed, resistance depends on ρ (resistivity).