Potential Dividers Gcse Coursework Markscheme
Fixed resistors in series
Potential dividers divide up the voltage within a circuit, so that parts of a circuit only receive the voltage they require. Potential dividers usually consist of two or more resistors arranged in series across a power supply.
Fixed resistor in series with an LDR
Potential dividers form an important part of sensor circuits. For example, an LDR [LDR: A Light Dependent Resistor, or LDR, is a type of resistor which is affected by changes in light levels. A cadmium sulphide layer causes a decrease in resistance in the light and increase in the dark. ] or thermistorthermistor: An electrical device whose resistance decreases as its temperature increases. can be used in place of one of the resistors, with the output voltage signal being directed to an op-amp [operational amplifier: A device which takes a relatively weak signal as an input and produces a much stronger signal as an output. ] or IC.
Variable resistor in series with a thermistor
Instead of using a fixed resistor, a variable resistor allows the output voltage to be adjusted. A low-value fixed resistor should be placed in series with the variable resistor to prevent the full power of the circuit from being routed down the output voltage path if the variable resistor is accidentally moved to a low resistance.
Common uses of potential dividers
Potential dividers are important in both transistor-switching circuits and op-amp comparator circuits [Comparator circuits: Circuit with a comparator - a component which compares two voltages and gives either a high or low output depending on the result of the comparison. ]. The diagram shows a darkness-sensor circuit with a transistor [transistor: Components which do not conduct electricity unless they are turned on by a (different) electrical current. This means they can be used as switches, amplifiers and in other ways. ] used as a switch. When the LDR senses a drop in light, the LED is switched on.
- When the LDR has light falling on it, its resistance is low, usually around 400 ohms.
- When the LDR is covered up, the resistance increases (often to many kilo-ohms).
When the resistance of the LDR is small, its share of the voltage supply is small too; this means that the output voltage (Vout) from the voltage divider is small and the transistor is switched off.
In the dark the large resistance of the LDR takes a large share of the voltage supply so Vout is large and the transistor and LED both switch on.
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This qualification is designed to prepare students for university study in physics or engineering.
Each module covers a topic that can be exemplified in many different applications, bringing the subject to life.
Students must carry out 10 required practical activities in the course. The practicals are not constrained, allowing each school to choose resources and equipment that best suit their circumstances.
Practicals in this specification include the Young modulus of a metal and investigations into interference effects, transformers and determination of g. Exam questions will be asked on the practicals, but there is no coursework or practical exam.
Physics is fundamentally a mathematical subject, and this is reflected in the requirement for students to develop a wide range of mathematical skills.
Examinations will include both shorter questions for quickly checking understanding and longer extended calculations, which allow students to demonstrate logical thinking. Extended writing questions allow students to demonstrate the depth of their knowledge. In addition, multiple choice questions are included at the end of the papers, allowing students to manage their time.
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Unit 1: Mechanics, materials and atoms (AS)
Unit 2: Electricity, waves and particles (AS)
Unit 3: Fields and their consequences (A2)
Unit 4: Energy and energy resources (A2)
Unit 5: Physics in practice and multiple choice (A2)
- Candidates may re-sit a unit any number of times.
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- Candidates who wish to repeat a qualification may do so by re-sitting one or more units.
Measurements and their errors
- Use of SI units and their prefixes
- Limitation of physical measurements
- Estimation of physical quantities
Mechanics and materials
- Scalars and vectors
- Motion along a straight line
- Projectile motion
- Newton's laws of motion
- Work, energy and power
- Conservation of energy
- Bulk properties of solids
- The Young modulus
Particles, radiation and radioactivity
- Constituents of the atom
- Elementary particles
- Basics of electricity
- Current - voltage characteristics
- Potential divider
- Electromotive force and internal resistance
Oscillations and waves
- Oscillating systems
- Forced vibrations and resonance
- Progressive waves
- Longitudinal and transverse waves
- Principle of superposition of waves and formation of stationary waves
- Refraction at a plane surface
- Collisions of electrons with atoms
- Photoelectric effect
- Wave particle duality
Circular and periodic motion (A-level only)
- Circular motion
- Simple harmonic motion
Gravitational fields and satellites (A-level only)
- Newton's gravitational law
- Gravitational field strength
- Gravitational potential
- Orbits of planets and satellites
Electric fields and capacitance (A-level only)
- Coulomb's law
- Electric field strength
- Electric potential
Exponential change (A-level only)
- Capacitor charge and discharge
- Exponential changes in radioactivity
Magnetic fields (A-level only)
- Magnetic flux density
- Moving charges in a magnetic field
- Magnetic flux and flux linkage
- Electromagnetic induction
- Alternating currents
- The operation of a transformer
Thermal physics (A-level only)
- Energy transfer by heating and doing work
- Energy transfer by conduction and radiation
- Ideal gases
- Kinetic theory of gases
Nuclear energy (A-level only)
- Radius of the nucleus
- Mass and energy
- Induced fission
- Safety aspects nuclear reactors
- Nuclear fusion
Energy sources (A-level only)
- Rotational motion
- Wind energy
- Solar energy
- Hydroelectric power and pumped storage
Practical and analytical skills (A-level only)
- Practical skills
- Data analysis skills
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