ELECTRICITY & MAGNETISM content

what is the role of a switch in a circuit?

a switch can open and close. when open, current can't flow in the circuit. when closed, it flows.

what is the role of a cell in a circuit?

provides the p.d to cause a current

what is the role of a battery in a circuit?

is many cells combined, meaning it can have any voltage

what is the role of a diode in a circuit?

allows current to flow through it in one direction only.

what is the role of a resistor in a circuit?

opposes the flow of charge and decreases current. it heats up as current through it increases

what is the difference between a variable and normal resistor?

you can change the amount of resistance

what is the role of an LED in a circuit?

diode that also emits light

what is the role of a lamp/bulb in a circuit?

there is a thin wire inside that gets very hot and lights up

what is the role of a fuse in a circuit?

a safety device: it is a thin wire that melts and breaks the circuit when current is too big

what is the role of a voltmeter in a circuit?

measures voltage (must be connected parallel)

what is the role of an ammeter in a circuit?

measures current (must be connected in series)

what is the role of a thermistor in a circuit?

also a resistor but resistance decreases as temperature increases

what is the role of an LDR in a circuit?

also a resistor but resistance decreases as more light hits it

what is inside a wire? (2)

positive lattice/metal ions and loose electrons

how is resistance caused?

positive lattice ions and loose electrons collide

what things are needed for current to flow? (2)

- completed circuit

- power source

what factors affect resistance in a wire? (4)

- diameter of the wire/thickness

- length

- material

- temperature

how does diameter of wire/thickness affect resistance?

thicker wire --> less resistance

how does length affect resistance?

longer --> more resistance

how does temperature affect resistance?

hotter --> more resistance

what are the 2 rules for current?

1. total current into a junction = total current out of a junction

2. the lower the resistance of a path, the more current it will get

what are the 2 rules for voltage?

1. total p.d into a closed loop from battery = total p.d used around the loop

2. when p.d is shared between 2 resistors, the larger the resistance, the greater the share of p.d

is resistance lower when resistors are in parallel or series and why?

parallel creates more routes for current. therefore, current increases and resistance decreases

how do you write the resistance for parallel circuits?

r < (the resistance of the weakest resistor)

in which component is the current and voltage ohmic?

resistor

what are the measurement prefixes and their power of 10?

Terra (T) - 10^12

Giga (G) - 10^9

Mega (M) - 10^6

Kilo (K) - 10^3

Mili (m) - 10^-3

Micro (μ) - 10^-6

Nano (n) - 10^-9

how do N & N or S & S poles interact?

repel

how do N & S or S & N poles interact?

attract

what are the 4 magnetic materials?

iron, cobalt, nickel, steel

what can induced magnets only attract?

permanent magnets

what does it mean if the lines on a magnetic field are closer together?

stronger

if i rub a plastic rod on a duster and then i put the rod under water, why does the water bend?

the electrons from the duster are transferred to the rod. the rod becomes negatively charged and the water is positively charged so they repel.

how is an electric field produced?

by electric charges

how does lightning happen?

1. friction acts between ice crystals in clouds

2. electrons are transferred between them and charge builds up

3. the top of the cloud is pos and bottom is neg

4. the ground (positive) and cloud have an electric field between them

5. the charge is so large that the air becomes a conductor through ionisation

6. current flows through the air as lightening

what does it mean if something is induced?

created

when is a magnetic field induced around a conductor?

when a current flows through an electrical conductor

how can you tell the direction of a magnetic field around a regular conductor?

using your right hand, hold the object. your thumb should point in the direction of conventional current. the other fingers show you the direction of the magnetic field lines?

how can you tell the direction of a magnetic field around an electromagnet?

hold the electromagnet with your fingers wrapped around in the direction of the current. the direction your thumb points is the North