Unit 4 Flashcards
What are the forces between magnetic poles and magnetic materials?
Like poles (e.g., N-N or S-S) repel, and unlike poles (e.g., N-S) attract. Magnetic materials are attracted to magnets.
What is the difference between magnetized and unmagnetized materials?
Magnetized materials produce their own magnetic field, while unmagnetized materials do not.
What is induced magnetism?
It occurs when a magnetic material is temporarily magnetized by being in a magnetic field.
What are the properties of temporary magnets?
Temporary magnets (e.g., soft iron) lose their magnetism when removed from the magnetic field.
What are the properties of permanent magnets?
Permanent magnets (e.g., steel) retain their magnetism after being magnetized.
What is the difference between magnetic and non-magnetic materials?
Magnetic materials (like iron, cobalt, nickel) can be magnetized, while non-magnetic materials (like wood, plastic) cannot.
What is a magnetic field?
A region in which a magnetic pole or material experiences a force.
How can the pattern and direction of magnetic field lines around a bar magnet be shown?
By sprinkling iron filings or using a compass to show the field lines from N to S pole.
How is the direction of a magnetic field at a point determined?
It is the direction of the force on the N pole of a magnet at that point.
How can you plot magnetic field lines?
Using a compass or iron filings, place them around the magnet and observe the lines.
What are some uses of permanent magnets and electromagnets?
Permanent magnets are used in fridge doors, compasses, and loudspeakers. Electromagnets are used in cranes, electric bells, and relays.
What causes magnetic forces?
They arise from interactions between magnetic fields.
What does the spacing of magnetic field lines indicate?
Closer spacing indicates a stronger magnetic field.
What are the two types of charges, and how do they interact?
Positive and negative charges; like charges repel, unlike charges attract.
How can you detect electrostatic charges?
By rubbing materials to generate static electricity and observing attraction or repulsion.
How does friction charge solids?
By transferring electrons (negative charges) between materials.
What is an experiment to distinguish between conductors and insulators?
Use a circuit with a bulb; conductors allow current to flow (bulb lights), insulators do not.
Give examples of electrical conductors and insulators.
Conductors: copper, aluminum. Insulators: plastic, rubber.
In what unit is charge measured?
Charge is measured in coulombs (C).
What is an electric field?
A region where a charge experiences a force.
What is the direction of an electric field at a point?
It is the direction of the force on a positive charge at that point.
Describe electric field patterns around a point charge.
Radial lines outward for positive, inward for negative.
Describe electric field patterns around a charged sphere.
Similar to a point charge.
Describe electric field patterns around parallel plates.
Uniform lines between plates, perpendicular to the surface.
What is the relationship between electric current and charge flow?
Electric current is the rate of flow of charge.
How is current measured?
Using ammeters (analogue or digital).
What is electrical conduction in metals?
It occurs when free electrons move through the metal, carrying charge.
What is the difference between direct and alternating current?
Direct current (d.c.) flows in one direction; alternating current (a.c.) reverses direction periodically.
Write the equation for current.
I = Q / t, where I is current, Q is charge, and t is time.
What is conventional current?
It flows from positive to negative, opposite to electron flow.
Define e.m.f.
The work done per unit charge by a source to move the charge around a complete circuit.
Define potential difference.
The work done per unit charge as it passes through a component.
How is e.m.f. or p.d. calculated?
E = W / Q, where W is work, and Q is charge.
Write the formula for resistance.
R = V / I, where R is resistance, V is voltage, and I is current.
What factors affect resistance in a wire?
Resistance is directly proportional to length and inversely proportional to cross-sectional area.
Write the formula for electrical power.
P = IV, where P is power, I is current, and V is voltage.
Write the formula for electrical energy.
E = IVt, where E is energy, I is current, V is voltage, and t is time.
What is a kilowatt-hour (kWh)?
The energy used by a 1 kW device in 1 hour.
What are the hazards of damaged insulation?
It can lead to electric shocks or short circuits.
What are the hazards of overheating cables?
It may cause electrical fires.
Why is dampness dangerous in electrical circuits?
Water conducts electricity, leading to electric shocks.
What are the hazards of overloading plugs or extension leads?
Excess current can cause overheating and fires.
What wires make up a mains circuit?
Live wire, neutral wire, and earth wire.
Why must a switch be connected to the live wire?
To safely disconnect the appliance from the high-voltage supply.
What is the purpose of trip switches and fuses?
To break the circuit when the current exceeds safe levels, preventing damage or injury.
Why must the outer casing of an appliance be non-conducting or earthed?
To prevent electric shock if the casing becomes live.
What is the purpose of a fuse in a double-insulated appliance?
To protect the appliance and cabling from excessive current.
