5 (a) A resistor is connected to a power supply - Edexcel - GCSE Physics Combined Science - Question 5 - 2018 - Paper 1

To find the time, we use the formula:

$t = \frac{Q}{I}$

Where:

• $Q$ is the charge (42 C)
• $I$ is the current (200 mA = 0.2 A)

Substituting the values:

$t = \frac{42 \, \text{C}}{0.2 \, \text{A}} = 210 \, \text{s}$

To convert seconds to minutes:

$t = \frac{210}{60} = 3.5 \text{ minutes}$

Thus, the time taken is 3.5 minutes.

The total energy transferred can be calculated using the formula:

$E = V \cdot Q$

Where:

• $E$ is energy (in joules)
• $V$ is the potential difference (6.0 V)
• $Q$ is the charge (42 C)

Substituting the values:

$E = 6.0 \, \text{V} \cdot 42 \, \text{C} = 252 \, \text{J}$

Therefore, the energy transferred is 252 J.

The resistor becomes warm due to the collisions between the charged particles (electrons) flowing through it and the atomic lattice of the resistor. As the electrons move, they collide with the lattice, causing it to vibrate. This increase in atomic vibration leads to a rise in temperature, resulting in the resistor becoming warm.

Given that the potential difference between P and Q is 6.0V and the current flowing is 1.2A, we can calculate the total resistance required using Ohm's law:

$R = \frac{V}{I} = \frac{6.0 \, \text{V}}{1.2 \, \text{A}} = 5 \Omega$

Since the total resistance calculated (5Ω) is less than the resistance of either of the two 100Ω resistors connected in series (which would be 200Ω), we deduce that the resistors must be connected in parallel.