2 c) energy and potential difference in circuits d) electric charge Flashcards
2.8 explain why a series or parallel circuit is more appropriate for particular applications, including domestic lighting
Series Circuit:
one switch can turn off the components on and off together
if one bulb ( or other component) breaks, it causes a gap in the circuit and all of the other bulbs will go off
the voltage supplied by the cell or mains supply is “shared” between all the components, so the more bulbs you add to a series circuit the dimmer they all become. The larger the resistance of the component, the bigger its “share of voltage”
Parallel Circuit:
switches can be placed in different parts of the circuit to switch each bulb on and off individually or all together
if one bulb (or other components) breaks, only the bulbs on the same branch of the circuit will be affected
each branch of the circuit receives the same voltage, so if more bulbs are added to a circuit in the parallel they all stay bright.
Decorative lights are usually wired in series. Each bulb only needs a low voltage, so even when the voltage from the mains supply is shared between them, each bulb still gets enough energy to produce light. The lights in our house are wired in parallel. Each bulb can be switched on and off separately and the brightness of the bulbs does not change.
2.9 understand that the current in a series circuit depends on the applied voltage and the number and nature of other components
In a series circuit the current is the same in all parts. Current is not used up as it passes around a circuit.
The size of the current is a series circuit depends on the voltage supplied to it, and the number and nature of the other components in the circuit. In a circuit if more cell is attached, the current will increase. If more resistance is attached to the circuit the current will get less. But current is same at all points in a series circuit.
2.10 describe how current varies with voltage in wires, resistors, metal filament lamps and diodes, and how this can be investigated experimentall
In parallel circuit, current varies with the resistance and voltage. Voltage are same at all branches.
http://shawonnotes.ucoz.com/IGCSE_Physics/physics_images/parallel-circuit.png
This circuit shows a 10 Ω and 20 Ω resistor connected in parallel to a 6V cell of negligible internal resistance. The p.d. across 10 Ω and 20 Ω resistors is 6V.
I1 = 0.6A
I2 = 0.3 A
As the resistance in I2 is higher, the current is small.
I3 = I1 + I2 (The current in a parallel circuit is shared between the branches depending on the resistance.)
2.11 describe the qualitative effect of changing resistance on the current in a circuit
Resistance is inversely proportional to current. Higher resistance means lower current and higher current means lower resistance. In other words resistance is the opposite of current. Resistance blocks charge flow.
2.12 describe the qualitative variation of resistance of LDRs with illumination and of thermistors with temperature
An LDR is a light dependant resistor. Its resistance changes with the intensity of light. It has a high resistance in the dark but low in the light. A thermistor is a temperature dependant resistor. In hot conditions there will be less resistance but in cold conditions there will be high resistance.
2.13 know that lamps and LEDs can be used to indicate the presence of a current in a circuit
All lamp and LEDs emit light when current passes through them. If an LED or a lamp lights up when connected to a circuit, this shows that a current is present in the circuit.
2.14 know and use the relationship between voltage, current and resistance:
voltage = current × resistance V = I × R
2.15 understand that current is the rate of flow of charge
The size of an electric current indicates the rate at which charge flows. Charge(Q) is measured in coulombs (C). Current is measured in amperes (A). If 1 C of charge flows along a wire every second the current passing the wire is 1A.
2.16 know and use the relationship between charge, current and time:
charge = current × time Q = I × t
2.17 know that electric current in solid metallic conductors is a flow of negatively charged electrons
Current is the flow of charge. One coulomb of charge is equivalent of the charge carried by approximately six million, million, million (6 x 1018) negative electrons.
d) 2.18 identify common materials which are electrical conductors or insulators, including metals and plastics
Conductors: Electrical conductors are materials that allow current to pass through them. Conductors have free electron diffusion to pass current. Metals like copper, silver, aluminium have free electrons and can conduct electricity.
Insulators: Insulators do not conduct electricity because they don’t have free electrons. Example of insulator are plastics, rubber, wood etc.
