42- A student measures the potential difference across a device and the current in the device. $$ 28.0625 / 21 / \mathrm{M} / \mathrm{J} / 18 $$ Which calculation gives the resistance of the device? A current + potential difference B current $$ \div $$ potential difference C) potential difference $$ \div $$ current D potential difference $$ \times $$ current 43- A water heater is connected to a 230 V supply and there is a current of 26 A in the heater. It takes 20 minutes to heat the water to the required temperature. 29.0625/21/M/J/18 How much energy is supplied by the heater? A $$ 6.0 \times 10^{3} \mathrm{~J} $$ B $$ 1.0 \times 10^{4} \mathrm{~J} $$ C $$ 1.2 \times 10^{5} \mathrm{~J} $$ D $$ 7.2 \times 10^{6} \mathrm{~J} $$

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### **Question 42**

**Which calculation gives the resistance of the device?**

**Options:**
- A) Current $$ + $$ Potential Difference
- B) Current $$ \div $$ Potential Difference
- C) Potential Difference $$ \div $$ Current
- D) Potential Difference $$ \times $$ Current

**Solution:**

To determine the resistance ($$ R $$) of a device when you have the potential difference ($$ V $$) and the current ($$ I $$), you can use **Ohm's Law**, which is stated as:

$$
V = I \times R
$$

To solve for resistance ($$ R $$), rearrange the formula:

$$
R = \frac{V}{I}
$$

This means resistance is calculated by **dividing the potential difference by the current**.

**Correct Answer:**  
**C) Potential Difference $$ \div $$ Current**

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### **Question 43**

**A water heater is connected to a 230 V supply and there is a current of 26 A in the heater. It takes 20 minutes to heat the water to the required temperature. How much energy is supplied by the heater?**

**Options:**
- A) $$ 6.0 \times 10^{3} \mathrm{~J} $$
- B) $$ 1.0 \times 10^{4} \mathrm{~J} $$
- C) $$ 1.2 \times 10^{5} \mathrm{~J} $$
- D) $$ 7.2 \times 10^{6} \mathrm{~J} $$

**Solution:**

1. **Calculate Power ($$ P $$)**:
   
   Power is given by the product of voltage and current:
   
   $$
   P = V \times I = 230\, \text{V} \times 26\, \text{A} = 5980\, \text{W}
   $$

2. **Convert Time to Seconds**:

Energy calculations require time in seconds.
   
   $$
   20\, \text{minutes} = 20 \times 60 = 1200\, \text{seconds}
   $$

3. **Calculate Energy ($$ E $$)**:
   
   Energy is the product of power and time:
   
   $$
   E = P \times t = 5980\, \text{W} \times 1200\, \text{s} = 7,176,000\, \text{J}
   $$
   
   Which can be expressed in scientific notation as $$ 7.176 \times 10^{6} \mathrm{~J} $$.

4. **Match with Options**:
   
   The closest option is $$ 7.2 \times 10^{6} \mathrm{~J} $$.

**Correct Answer:**  
**D) $$ 7.2 \times 10^{6} \mathrm{~J} $$**

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**Question 42:** To find the resistance, divide the potential difference by the current. **Answer:** C) Potential Difference $$ \div $$ Current **Question 43:** Calculate energy using power and time. **Answer:** D) $$ 7.2 \times 10^{6} \mathrm{~J} $$

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