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Electricity — Science STD 10 — Question

Maharashtra BoardEnglish MediumSTD 10ScienceElectricity4 Marks
Question
The table below shows the current in three different electrical appliances when connected to the 240V mains supply:
Appliance Current
Kettle 8.5A
Lamp 0.4A
Toaster 4.8A
  1. Which appliance has the greatest electrical resistance? How does the data show this?
  2. The lamp is connected to the mains supply by using a thin, twin-cored cable consisting of live and neutral wires. State two reasons why this cable should not be used for connecting the kettle to the mains supply.
  3. Calculate the power rating of the kettle when it is operated from the 240V mains supply.
  4. A man takes the kettle abroad where the mains supply is 120V. What is the current in the kettle when it is operated from the 120V supply?
✓

Answer

  1. Lamp; because least current is flowing through it.
  2. Large current drawn by the kettle; Earth connection needed.
  3. We know that
P = VI

V = 240V, I = 8.5A

P = 240 × 8.5 = 2040W = 2.04kW
  1. When connected to 240V supply, P = 2040W
R = $\frac{\text{V}_2}{\text{P}}=\frac{2402}{240}$

R = 28.23 ohm

Now, when V = 120V, R = 28.23 ohm

$\text{I}=\frac{\text{V}}{\text{R}}=\frac{120}{28.23}=4.25\text{A}$​​​​​​​

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