The circuit in the diagram contains an LED in series with a light-dependent resistor (LDR) - Junior Cycle Science - Question b - 2014

The device labelled Y is a voltmeter. It is designed to measure the potential difference (voltage) across two points in a circuit, usually expressed in volts (V).

The letters LED stand for Light Emitting Diode. It is a semiconductor device that emits light when current flows through it.

To plot the graph, plot the resistance values (Ω) on the y-axis against the distance (cm) on the x-axis. Ensure to accurately represent the points:

• (10 cm, 200 Ω)
• (20 cm, 800 Ω)
• (30 cm, 1800 Ω)
• (40 cm, 3200 Ω)
• (50 cm, 5000 Ω)

Draw a smooth curve connecting the points to show the trend.

From the graph, it can be observed that as the lamp is moved away from the LDR, the resistance of the LDR increases. This is due to the decrease in light intensity reaching the LDR, causing it to resist the flow of current more as the distance increases.

Using the graph, the estimated resistance of the LDR when the lamp is placed 25 cm away is approximately 1200 Ω, based on the plotted values.

Using Ohm's Law, which states that voltage (V) = current (I) × resistance (R), we can rearrange the formula to calculate current:

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

Substituting the values, we have: $I = \frac{6 \text{ V}}{1200 \Omega} = 0.005 \text{ A}$

Thus, the current flowing through the LDR is 0.005 A.

An LED is more efficient than a standard light bulb because it requires less current to produce the same amount of light. LEDs convert a higher proportion of electrical energy into light rather than heat, whereas traditional incandescent bulbs waste much of their energy as heat. This results in lower energy consumption and a longer lifespan for LEDs compared to standard light bulbs.