§ A light bulb gives out light when electricity passes through it
§ The more volts you add, the more intense the light is. As you double
the voltage, the light intensity doubles.
§ This is because the rays are more concentrated. The rays are twice
as concentrated as the intensity doubles, as more power is running
through the circuit
§ The LDR (Light dependent resistor) measures how intense the light is
§ The LDR frees up electrons, decreasing resistance
§ The more intense the light is, the lower the resistance in the LDR
§ Ohms law says that current increase is proportional to potential
§ This only occurs if all conditions are the same
§ As Potential difference doubles, Current doubles.
§ Resistance is voltage over current.
§ If voltage rises proportionally with current, then resistance will
halve as voltage doubles.
§ So as I halve the voltage, the current halves, light intensity
halves, and resistance doubles.
This is how I will set up the apparatus. Below is a circuit diagram.
The set up of the circuit is simple as shown above. The 12-volt lamp
is set up in a simple circuit. Then in a SEPARATE circuit, the light
dependent resistor is connected to the Multimeter, which shows the
resistance readings. If I did connect the LDR in the same circuit, I
would almost certainly fry the LDR, and ruin the experiment! I want to
keep the distance from the lamp to the LDR the same. I have decided
after testing the system, to put the LDR directly under the lamp. This
makes me get the best readings for the earlier voltages when the bulb
is dim. It also helps to cancel out any other light, which will
obviously get in the way more, the further the LDR is from the bulb. I
will find out how much this effects the results in the preliminary
I will needed to keep the bulb at a set height, perhaps 2cm above the
LDR. During the preliminary practical, there are many things I can do
to get the optimum results. That includes keeping the distance and
height the same, but also taking the correct resistance reading. You
can set the resistance readings on the Multimeter to different levels
of accuracy. If you don't have a large enough setting, the dial will
display one. I will then go down one until I get a suitable answer. I
may even have to change the accuracy settings during the preliminary
practical, if they become too inaccurate. My independent variable is
voltage (potential difference). I will be finding out how the
intensity of the light effects resistance of the LDR. I will be going
up in gaps of 2 volts, up to 12 or 14 volts, giving me seven readings.
I need to make sure I get two, preferably 3 sets of good results, to
iron out anomalies, getting a better overall average.