IGCSE Electricity Flashcards
Describe the structure of an atom
Nucleus contains positively charged protons and neutral neutrons.
Negative electrons orbit the nucleus.
How do objects become Negatively Charged?
• Electrons are transferred to the rod by friction.
• As the rod gains electrons it becomes negatively charged.
(NB The cloth loses electrons and becomes positively charged)
How do objects become Positively charged?
• Friction removes electrons from the rod.
• As the rod looses electrons it becomes positively charged.
(NB The cloth gains electrons and becomes negatively charged.)
How do Opposite Charges Behave?
Opposite charges ATTRACT.
How do Like Charges Behave?
Like charges REPEL
What happens to the resistance of a bulb as current increases.
The resistance of a lamp increases as the temperature increases.
How does the resistance of a Thermistor change?
Low resistance when hot
High resistance when cold
How does the resistance of a Light Dependant Resistor (LDR) change?
Low resistance when light
High resistance when dark
What does an Ammeter measure and where should it be placed in a circuit?
An ammeter must be connected in series as it measures the current flowing through it.
Current is measured in Amps
What does a Voltmeter measure and where should it be placed in a circuit?
A voltmeter must be connected in parallel as it measures the potential difference across the component.
What is Ohm’s law?
The current is directly proportional to the voltage.
Fixed resistors and wires at constant temperature obey Ohm’s law.
What is the function of a diode?
A diode allows current to flow in one direction only.
It has very high resistance to current in the reverse direction.
What is the rule for currents in a parallel circuit?
The total current through the circuit is the sum of the current through the separate branches.
What is the rule for currents in a series circuit?
The current is the same all the way around a series circuit.
What is the rule for potential difference in a parallel circuit?
The potential difference across each branch is the same in a parallel circuit.
What is the rule for potential difference in a series circuit?
In a parallel circuit the potential difference across each component adds up to the battery potential difference.
What are some advantages of a parallel circuit?
In a parallel circuit:
• Switches can be used to control individual bulbs
• If one bulb breaks only the bulbs in the same branch will be affected
• Each bulb receives the same voltage so they if more are added they all stay bright.
What are some disadvantages of a series circuit?
In a series circuit:
• If one bulb breaks they all go out (Christmas tree lights)
• One switch can be used to control all bulbs
• Voltage is shared so the more bulbs there are the dimmer they become.
What is the definition of current?
Current is the rate of flow of charge.
What is the definition of potential difference?
The potential difference across an electrical component is the electrical energy supplied to it per coulomb of charge flowing through it.
What is the definition of emf?
The emf of a batter is the electrical energy it produces per coulomb of charge.
What happens to the resistance of a wire if its cross sectional area is increased?
The larger the cross sectional area, the lower the resistance.
What happens to the resistance of a wire if the length is increased?
The longer the wire the higher the resistance.
