P4 electric circuits Flashcards
(35 cards)
What charges are protons, electrons and neutrons?
A proton is positive
A electron has an equal negative charge
A neutron is uncharged
What are uncharged and charged atoms made of and called?
An uncharged atom has equal numbers of electrons and protons. A charged atom is called an ion
What is a negative and positive ion?
A negative ion is where you add electrons to uncharged atoms because the atom has more electrons than protons. A positive ion is where you remove electrons from an uncharged atom making it a positive ion because the atom has fewer electrons than protons.
How can insulators become charged?
When you rub them with another insulator such as a dry cloth. While rubbing the insualtor, electrons are transferred from one of the materials to the other material.
What force is exerted between charged objects and why?
They exert a non-contact force. This is because one of the charged objects creates an electric field around itself. The second charged object in the field experiences a force because of the field. The field, and therefore the force between the two charged objects becomes stronger as the distance between the objects decreases.
What would happen if the two objects are negatively charged?
Electrons in the air molecules between the two objects experience a force towards the positive object. However if the field is too strong sparking happens because some electrons are pulled out of air molecules because of the force of a field, knocking into other air molecules pulling the electrons out of them, creating a sudden flow of electrons between two charged objects.
What are the symbols of components in a circuit?
Look at page 52
What is an electric current and how does it work?
An elecric current is a flow of charge. When a circuit is on millions of electrons flow through every second. Each electron contains a negative charge. Metal, a conductor contains lots of electrons that move around freely between the positive charge metal ions. These electrons stop the ions moving away from eachother.
What is the size of a electric current?
The rate of flow of electric charge. This is the flow of charge per second. The bigger the number of electrons that pass through a component each second, the bigger is the current passing through it.
How is electric charge and electric current measured?
Electric charge is measured in coulombs(C).
Electric current is measured in amperes(A).
How to measure charge?
charge flow,Q(coulumbs,C)=current,I(amperes,A)x time taken,t(seconds,s)
What does an ammeter do?
It measures the current. It is connected in a series with a bulb for example, so the current through them is the same. The ammeter reading tells you the current in amperes.
What does a voltmeter do?
It measures potential difference. This is the energy transferred to the bulb for example or the work done on it by each coulomb of charge that passes through it. When the voltmeter is connected in parallel with a bulb it measures the potential difference across it.
How do you find potential difference/volts?
potential difference across a component, V(volts, V)= energy transferred,E(joules,j) ÷ charge, Q(coulumbs, C)
What does a resistor do?
The unit is the ohm and the resistor in a circuit limits the current. The larger the resistance of a resistor, the smaller the current. If you reverse the potential difference across a resistor it reverses the current through it.
How to find resistance and resistance of an appliance?
resistance, R(ohms) = potential difference, V(volts, V) ÷ current, I(amperes,A)
What is Ohms law?
Ohms law is the current being directly proportianal to the resistance. In other words the resistance is constant.
What does a current-potential difference graph show?
The line curves away from the y-axis. So therefore the current is not directly proportional to the potenial difference. The lamp for example is a non-ohmic conductor.
What makes a filament lamps resistance increase?
If the current increases, it’s temperature increases because of the atoms vibrating. This means they resist the passage of the electrons through the filament more. The resistance of any metal increases with temperature.
What happens if you reverse the potential difference?
It reverses the current and makes no difference to the shape of the curve. The resistance is the same for the same current regardless of it’s direction.
What does a current poential difference graph for a diode show?
It shows the current through a diode only flows one way, called the forward direction. In this forward direction, the line curves towards the y-axis. So the current is not directly proportional to the potential difference. In the reverse direction, the current is virtually zero. So the diode’s resistance in the reverse directon is a lot higher than its resistance is in the forward direction.
What is a thermosistor and light dependent resistor.
A thermisistor is a resistor that depends on temperature and its resistance decreases if the temperature increase and vice versa. The resistance of a light dependent resistor(LDR) decreases if the light intensity increases and vice versa.
How does the current and total potential difference disperse around a series circuit?
The same current passes through each component every second. In a series circuit, the total potential difference of the power supply(voltage) is shared between the components.
What happens with cells in series?
The total potential difference of cells in series is the sum of the potential difference of each cell.
