P3 Flashcards
What is electric charge?
A property of matter that can be positive or negative.
When is a body neutral?
When it has equal positive and negative charges.
What happens with like and unlike charges?
Like charges repel; opposite charges attract.
What are insulators?
Materials where charged particles are fixed and cannot flow—do not conduct charge.
What are conductors?
Materials with delocalised charged particles that can flow—can conduct charge.
What happens when two insulators are rubbed together?
Electrons transfer—one object gains electrons (negative), the other loses (positive).
Why don’t conductors build static charge when rubbed?
Electrons flow in and out, cancelling out charge.
What causes a spark?
When enough charge builds up and the objects are close but not touching p.
What is electrostatic force?
A non-contact attractive or repulsive force between charge
What affects the strength of electrostatic force?
Greater charge and smaller separation (inverse square law)
What happens when a charged object is near a neutral one?
It induces a charge in the neutral object, attracting it.
Give an example of electrostatic attraction in real life.
stream of water bends toward a charged object (like a balloon)
What direction do electric field lines point?
Away from positive, towards negative charges.
What does more field lines indicate?
A stronger charge and stronger force.
What are the conditions for current to flow?
A closed circuit and a source of potential difference.
What pushes current through resistance?
Potential difference (voltage).
What is the formula for charge?
Q = I × t (charge = current × time)
Is current the same in a closed loop?
Yes—same at any point in a single, closed circuit.
What is potential difference (p.d)?
The energy transferred per unit charge, measured in volts (V).
How is p.d. measured?
Using a voltmeter placed in parallel across a component.
What is electric current?
The rate of flow of charge (electrons), measured in amperes (A).
How is current measured
With an ammeter placed in series in the circuit.
What is a series circuit?
A closed circuit with only one path for current—same current everywhere.
What is a parallel circuit?
A branched circuit—current splits into paths, but voltage stays the same across each branch.
What is the formula linking voltage, current, and resistance?
V = I × R (Voltage = Current × Resistance)
What does a linear I-V graph indicate?
Constant resistance. - ohm’s law if followed
What causes a non-linear I-V graph?
Changing resistance due to heat, current, or wire length.
What happens to resistance as current increases?
Electrons have more energy → collide with atoms → atoms vibrate more → resistance increases.
- current flow is reduced
What happens to resistance with increasing temperature in normal wires?
It increases due to increased atomic vibrations.
What happens to resistance in a thermistor as temperature increases?
Resistance decreases — useful in thermostats.
How does wire length affect resistance?
Longer wire = more resistance; current decreases
electrons face more obstacles, have to pass through more atoms
How does cross-sectional area affect resistance?
Thinner wire = higher resistance; less space for electrons to flow.
What happens to resistance in an LDR as light increases?
Resistance decreases — highest resistance when dark.
What is the function of a diode?
Allows current to flow in one direction only; very high resistance in the other direction.
What is a use of a diode?
Converting AC to DC.
What must you avoid during electrical experiments?
Overheating components — let them cool between readings.
How do you test resistance with different wires?
Use wires (1Ω–10Ω), connect to 2–12V DC, measure current and voltage, and plot I-V graph.
What is important about other wires in the circuit when measuring resistance?
They should have negligible resistance
How do you test a filament lamp?
Vary voltage (2–12V), measure current, plot I-V graph — shows non-linear resistance.
How do you test a diode?
Measure current for positive and negative voltages (e.g. 1 to -4V), plot I-V graph - shows current only flows in one direction
How do you test an LDR?
Shine light at different distances (10–50cm), measure current/resistance, and plot resistance vs light intensity.
How do you test a thermistor?
Place in water from 0ºC–60ºC, measure current, calculate resistance, and plot resistance vs temperature.
What happens to current in a series circuit?
It flows through all components equally.
What is the total resistance in a series circuit?
The sum of all component resistances.
Why is total resistance in series greater?
The charge must push through all items (resistors) .
How are components connected in a parallel circuit?
Each component is connected separately to the power supply.
What happens to total resistance in a parallel circuit?
It is less than the resistance of the smallest individual resistor.
Why does resistance decrease in parallel circuits?
Charge splits across multiple paths, reducing overall resistance.
What is the formula for electrical power?
Power = Voltage × Current → P = V × I
What is the alternate formula for power using resistance?
P = I² × R
What is the unit of power?
Watts (W)
What is the formula for energy transferred (using charge)?
Energy = Charge × Voltage → E = Q × V
What is the formula for energy using power and time?
Energy = Power × Time → E = P × t
What are the units of energy?
Joules (J)
How to calculate resistance in a parallel circuit?
as the sum of reciprocals of resistance
1/R(total) = 1/R(1) + 1/R(2) + …
What is the spark?
A discharge where charge jumps through the air to balance out.
