Physics Isa

5718 Words23 Pages
Introduction
I have chosen to investigate a factor that affects the output of a potential divider circuit. A potential divider is resistors connected in series across a voltage source; used to obtain a desired fraction of the voltage. A resistor is a device having resistance to the passage of an electric current which affects the output voltage (Vout). The factors that I could investigate are changing the resistance of r2 and record the output (Vout), or use a light-dependent resistor (LDR) and change the resistance of r2 and record the output (Vout).
Theories
Resistors restrict or limit the flow of current in a circuit. The ability of a material or component to resist current flow is measured in ohms. There are three main types of
…show more content…
Its value decreases with increasing incident light intensity. An LDR is made of a high-resistance semi-conductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistance.
A photoelectric device can be either intrinsic or extrinsic. In intrinsic devices, the only available electrons are in the valence band, and hence the photon must have enough energy to excite the electron across the entire bandgap. Extrinsic devices have impurities added, which have a ground state energy closer to the conduction band – since the electrons don’t have as far to jump, lower energy photons (i.e. longer wavelengths and lower frequencies) are sufficient to trigger the device.
Two of its earliest applications were as part of smoke and fire detection systems and camera light meters. Because cadmium sulphide cells are relatively inexpensive and widely available, LDRs are used in electronic devices that need light detection capability, such as security alarms, street lamps, and clock radios.
References:
* http://www.bbc.co.uk/schools/gcsebitesize/design/electronics/componentsrev4.shtml * School science text book

Prelims:
I aim to carry out two preliminary investigations to
Get Access