A resistor is connected to a power supply - Edexcel - GCSE Physics - Question 8 - 2018 - Paper 1

To find the time taken for a charge of 42C to flow through the resistor, we use the formula:

$Q = I imes t$ Where:

• Q = charge in coulombs (42C)
• I = current in amperes (200 mA = 0.2 A)
• t = time in seconds.

Rearranging for t gives: $t = \frac{Q}{I} = \frac{42}{0.2} = 210 \text{ seconds}.$ Converting seconds to minutes: $\frac{210}{60} = 3.5 \text{ minutes}.$. Therefore, the time taken is 3.5 minutes.

The energy transferred by the power supply can be calculated using the formula:

$E = V imes Q \text{ , where:}$

• E = energy in joules
• V = potential difference (6.0V)
• Q = charge (42C)

Substituting the values: $E = 6.0 imes 42 = 252 ext{ joules.}$

The resistor becomes warm because electrical energy is transformed into thermal energy due to collisions between the flowing electrons and the lattice structure of the resistor. As electrons pass through, they collide with atoms, causing them to vibrate more, increasing the kinetic energy of the lattice and resulting in heat production.

We know the total resistance can be calculated using Ohm's law:

$R = \frac{V}{I} = \frac{6.0 \text{ V}}{1.2 \text{ A}} = 5 \text{ ohms}.$

Since each resistor has a resistance of 100 ohms, they cannot be in series, as this configuration would yield a total resistance much greater than 5 ohms. Hence, the resistors must be arranged in parallel, where:

$\frac{1}{R_{total}} = \frac{1}{100} + \frac{1}{100} = \frac{2}{100} \Rightarrow R_{total} = 50 \text{ ohms}$

This analysis allows us to conclude that resistors are connected in parallel to achieve a total resistance that supports the current observed.