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level: Level 1

Questions and Answers List

level questions: Level 1

Question	Answer
Elementary charge (e): the “size” of the charge on a proton or electron Coulomb (C): SI unit 1 C = combined charge of 6.2x10^8 protons - 1 proton has a charge of +1.61x10^-19 C - 1 electron has a charge of -1.61x10^-19 C	Measuring charge
5 x -1.6x10-19 = 8 x 10-19 C The net charge on an object is -3.0μC. Calculate the number of extra electrons on the object. -3.0μC = -3.0x10-6 C ne = ?/(−?)	Calculate the charge on 5 electrons.
It is the movement of electrons that creates electrical effects. Materials where electrons that are weakly attracted to their nuclei can “jump” between atoms and move through a material.	Electrical conductivity
Electrons are held tightly to their nucleus and cannot easily move between atoms.	Electrical insulators
Answer:	Circuit diagram - match name to symbol
Symbol: I Unit: Ampere/Amps, A A measure of the number of electrons that pass through a point per second. I = Q/t I = Current (A) Q = Charge (C) t = Time (sec)	Current
Q = ne x qe Therefore..	Calculating the number of electrons that flow through a certain point.
ne = (? x ?)/qe ne = 20 x (30 x 60) /−1.6x10^−19 ne = 2.25x10^23 electrons	Calculate the number of electrons that pass through a point with 20 A over 30 min.
A chemical reaction within battery drives electrons to the negative terminal. Electrons repel each other. The repulsive force pushes them out of the battery and through the wire. Electrons are attracted to the positive terminal, this draws electrons into the battery. Energy is transformed from chemical to electrical potential energy.	Batteries - how do they work?
Stored as a separation of charge between terminals of a battery and provides energy to the circuit.	Electrical potential energy
Symbol: V Unit: Volts (V) 1 V = 1 JC-1 The difference in electrical potential energy across a component. The charge will flow until the potential difference is equal to zero. V = ?/? V = potential difference (V) E = electrical potential energy (J) Q = charge (C)	Potential difference
V = 10 V E = ? Q = 5 C E = 50 J	Calculate the amount of electrical potential energy carried by 5 C of charge at a potential difference of 10 V.
V = E/Q + I = ?/? Therefore: E = VIt E = energy provided by circuit = work done (J) V = potential difference (V) I = Current (A) t = time (s)	Work done by a circuit
E = ? V = 12 V I = 0.75 A t = (5 x 60) = 300 s E = 2700 J	A potential difference of 12 V is used to generate a current of 750 mA to heat water for 5 minutes. Calculate the energy transferred to the water in that time.
Electrical power = rate of doing work We know P = E/t and E = Vit Therefore: P = VI	Power
P = ? V = 120 V I = 6 A P = 720 W	An appliance running on 120 V draws a current of 6 A. Calculate the power used by this application.
Symbol: R Unit: Ohms (Ω) A measure of how hard it is for current to flow through a particular material. Yes As electrons “bump” into ions so they will need an energy boost (from the power source) to keep going. This boost needs to be greater than the resistance of the object or electrons will not flow.	Resistance
V = I R V = Potential difference (V) I = Current (A) R = Resistance (Ω)	Ohms Law for a constant temperature
V = 240 I = 10 R = ? R = 24 Ω	An electric heater draws 10 A of current when connected to a 240 V power supply. Calculate the resistance of the element in the heater.
Objects that obey ohms law. They are called resistors. Ohmic resistors are used to control the amount of current in a circuit. If the potential difference is doubled, then the current will also double. Will have straight-line V-I graphs, as they are proportional.	Ohmic conductors
Do not follow ohm’s law Do not have a straight line V-I graph. Resistance is not constant.	Non-ohmic conductors
Each component is dependant on the other (if one breaks, the circuit is broken, no flow of charge). Current is the same throughout the components of the circuit. Voltage is shared throughout the components of the circuit.	Series circuit
Allow for greater control of individual components (if one “line” breaks, the others still function). Current is shared throughout the components of the circuit. Voltage is the same throughout the components of the circuit.	Parallel circuit
Parallel, as each is provided with an equal potential difference.	Consider a scenario where you have two circuits. Each circuit has two light bulbs. Circuit A has the light bulbs connected in series, circuit B has them connected in parallel. In which circuit will the light bulbs shine brightest?
Definition: The sum of the resistance in all components within a circuit. Series: Parallel: RT = R1 + R2 + R3 etc. 1/RT = 1/R1 + 1/R2 + 1/R3 etc. Complete STAWA sets for practice.	Effective resistance
Components that can be manipulated to change the voltage across another component. Potentiometer: a sliding or turning object known as a wiper will alter the amount of resistance it provides. Thermistor: alters the amount of resistance depending on the temperature. - PTC: positive terminal coefficient, will increase resistance with temperature. - NTC: negative terminal coefficient, will decrease resistance with increased temperature.	Voltage dividers
Derived form V=IR Vout = Vin x R2/(R1 + R2)	Voltage dividers (don't need it but it's easier)
Three pins: - Active and Neutral: carries current to and from the device active: red/brown neutral: black/blue - Earth: connects the circuit through the ground. colour: green or green & yellow	Home circuits
When there is little to no resistance or no insulation between the active and neutral wires. Heat generated can cause electrical fires.	Short circuit
Interrupt the flow of current if it exceeds a set value.	Fuses and circuit breakers
Third pin of a plug. It's connected to the metal case/part of the appliance so if the active wire touches the case it will create a short circuit straight to the ground. This will involve a large current that will trip the circuit breaker.	Earth wires
Detect any difference between the current in the active and neutral wires. If it's not equal, the current must be “leaking” either into the earth wire or a person. It takes 20 milliseconds to switch off the current.	Residual current device (RCD)
The effect of an electric shock depends on: - the amount of current passing through the body - the duration - the path it takes What happens? Bodies are poor electrical conductors, large resistance will convert this energy into heat causing internal and external burns. If the current passes through your heart, 80 mA is enough to stop it beating.	Electric shock
AC = Alternating current: household current. Electrons oscillate back and forth to pass on energy. DC = Direct current: current provided by batteries. Electrons move through a wire from one terminal to another.	AC and DC