Topic 4 - Electric Circuits. Flashcards
What makes up the nucleus of an atom?
Protons and Neutrons.
What charge does a proton have?
Positive.
What charge does an electron have?
Negative.
What charge does a neutron have?
Neutron.
A charged atom is called an?
Ion.
When you rub a polystyrene rod on a towel, why does it become charged?
Electrons are transferred to the surface of the rod, so the polystyrene rod becomes charged.
Why do two negatively charged objects repel each other?
Because like charges repel.
Why does a negatively charged side of a magnet and a positively charged magnet pull towards each other?
Because unlike charges attract.
What is an insulator in electricity?
A substance that is poor at conducting electricity.
What is a conductor of electricity?
A substance that conducts electricity well.
What is static electricity?
Where electrons are transferred from one surface, where the surface they are transferred from is negatively charged and the position they are transferred to is positively charged. This is a non-contact force.
What is an electrical field?
An area around a charged surface that makes the force a non-contact force.
Do field lines go to or away from negatively charged fields.
Field lines go towards negatively charged fields.
Do field lines go to or away from positively charged fields?
Field lines go away from positively charged fields.
What are bulbs used for?
Producing light when a circuit is complete.
What are voltmeters used for?
Measuring the voltage produced by a power supply.
What are ammeters used for?
Measures the flow of electrons in a circuit or current.
What are resistors used for?
Slowing down the flow of electrons in a circuit or increasing resistance.
What does a variable resistor do?
It slows down the flow of electrons through a circuit like in a resistor but the resistance value can be changed.
What does a cell do?
Transfers chemical energy into electrical energy.
What is a battery?
Two or more cells in a series.
What does it mean if a circuit is closed?
The circuit is broken, no current will flow.
What does it mean if a circuit is closed?
The components in a circuit are connected, charge can flow.
What does a thermistor do?
Changes resistance depending on the temperature of the circuit.
What does an LDR do?
Changes resistance depending on light intensity. The higher the light intensity the lower the resistance and the more current will flow.
What does a diode do?
Only allows current to flow in one direction.
What is a fuse used for?
Used for cutting off a circuit when there is an overload of electricity.
What is a Light Emitting Diode (LED) used for?
Emits light when a current passes through it.
What the size of current called?
The rate of flow of charge.
What letter is associated with charge?
Q
What is the unit of charge?
Coulombs.
What is the unit of current?
Amperes or amps.
What is the equation for charge?
Charge (C) = Current (A) x time (s) or Q = It
What is potential difference?
The amount of energy transferred, per unit charge, transferred between two points in a circuit.
What is another name for potential difference?
Voltage.
What is Ohm’s law?
Resistance (Ohms) = Potential Difference (V) / Current (A).
Also shown as R = V/I
What is the units of voltage?
Volts.
If I have two resistors in a circuit and resistor 1 has 5 ohms of resistance and resistor has 10 ohms of resistance, what is the total resistance of the circuit? Using this value and the equation for Ohm’s law, figure out the voltage of the circuit of the current is 2 Amps.
There is a total resistance of 15 ohms. Ohms law = R = V / I and therefore 15 = V / 2. 15 x 2 = 30 volts.
If an ammeter has a reading of 0.1 A and the resistor has a resistance of 45 ohms what is the voltage of the circuit?
V = IR - V = 0.1 x 45 = 4.5. Voltage = 4.5 volts.
Is a resistor ohmic?
Yes, the amount of potential difference is directly proportional to the resistance of the device when at a constant temperature.
Is a filament bulb ohmic or not, if so why?
It isn’t ohmic because its resistance increases as the temperature of its filament increases so the current flowing in a filament bulb is not directly proportional to the voltage across it.
Is a semiconductor or diode ohmic or not and why?
It isn’t ohmic as the current only flows in one direction and the voltage isn’t directly proportional to its resistance.
Give an example of a diode.
An LED (Light Emitting Diode).
Ammeters are always connected in _______ and voltmeters are always connected in ________. Finish the sentence with two words and explain why you have chosen them.
Ammeters are always connected in series because they measure current and current is the same in series circuits. Voltmeters are always connected in parallel because voltage is the same in parallel.
Directly proportional diagrams always go through what point on a graph?
The origin.
What does it mean if a device follows Ohm’s law?
It’s current and voltage are directly proportional.
What happens when temperature increases in a circuit?
The ions gain more energy to move through the circuit and therefore current increases whilst resistance decreases.
For LDRs and thermistors, what happens to resistance when more heat is supplied?
The resistance decreases.
A semiconductor is usually found in what group of the periodic table meaning that when you increase temperature what happens?
When you heat a semiconductor resistance decreases as they are in group 4 and many electrons become delocalised, increasing current.
What is the equation that links Voltage, Energy Transferred and Charge?
Potential Difference (V) = Energy Transferred (J) x Charge (C) or in short hand- V = E / Q
What is the rearranged version of the equation linking voltage, energy and charge with energy as the subject?
Energy (J) = Charge (C) x Voltage (V) or E = QV
What is the equation that links Charge, Current and Time?
Charge (C) = Current (A) x time (s) or Q= It.
Voltage ____ ___ in parallel. What words finishes the sentence?
Adds up.
Voltage is _____ ____ in parallel, what word finishes the sentence?
The same.
Current is the same in _______. What word finishes the sentence?
Series.
Current is _____ in parallel. What word finishes the sentence?
Split.
Resistance ____ __ in series. What words finish the sentence and why?
Adds up because current has to travel through both resistors.
Resistance is ____ in parallel. What word finishes the sentence and why?
Resistance is less in parallel because there are more paths for current to pass through.
