National 5 Physics | Electricity | Section 2: Electrical Energy and Power

A microphone is an _____ device and converts _____ energy into _____ energy.

Input; sound; electrical

A solar cell is an _____ device and converts _____ energy into _____ energy.

Input; light; electrical

What is the relationship between temperature and resistance in a conductor?

When the temperature increases, the resistance also increases.

What is the relationship between temperature and resistance in a thermistor?

When the temperature increases, the resistance decreases.

What is the relationship between light level and resistance in a light dependent resistor?

When the light intensity increases, the resistance decreases.

Capacitor

Capacitors ==store electric charge==. The unit of capacitance is the farad (F).

When the lead is connected across a capacitor, it is said to be _____ and the voltage across it is _____.

Discharged; zero

When a capacitor is connected to a battery, it takes _____ for the voltage across it to rise. When full, it is said to be _____ and the voltage across it is equal to the _____ _____.

Time; charged; supply voltage

The resistance of a switch is very _____ when open and very _____ when closed.

High; low

Reed switch

A ==magnetically operated switch==. The contacts are usually open, and close when a reed relay (electromagnet) is brought close.

Reed relay

A ==coil carrying an electric current== (an electromagnet) can be used instead of a magnet to close the reed switch contacts.

The relay is an _____ device that changes _____ energy into the opening or closing of a switch. Reed relays can be used in _____ _____ _____.

Output; magnetic; high voltage systems

Lamps require a _____ current and get _____ in operation. It can still _____ when the connections to it are reversed.

Large; hot; function

Light emitting diodes (LEDs) only light if it is connected so that it points from a _____ voltage to a _____ voltage.

Positive; negative

LEDs require a _____ current to operate properly and _____ get hot in operation. They do not light if the connections to it are _____.

Small; won’t; reversed

State attributes of the LED: (5)

\-Needs less voltage/current

\-Lasts longer than regular lamps

\-Does not get hot unlike filament lamps

\-Only works with one direction of current

\-Must always be connected in series with a resistor (to limit current)

A loudspeaker is an _____ device and converts _____ energy into _____ energy.

Output; electrical; sound

A motor is an _____ device and converts _____ energy into _____ energy.

Output; electrical; kinetic

An element is an _____ device and converts _____ energy into _____ energy.

Output; electrical; heat

A buzzer is an _____ device and converts _____ energy into _____ energy.

Output; electrical; sound

Transistor

A transistor is an ==electronic switch==. They switch on when the input voltage exceeds a set value.

NPN transistor

B- base

C- collector

E- emitter

MOSFET transistor

G- gate

D- drain

S- source

NPN transistors are off (non-conducting) until the voltage is equal or above _____V (conducting).

0\.7V

MOSFET transistors are off (non-conducting) until the voltage is equal or above _____V (conducting).

2\.4V (according to SQA questions)

Power

The energy transferred in one second per unit time, ie. joules per second. 1 joule/s = 1 watt

The power rating of an appliance tells us how much _____ it transfers in _____ _____.

Energy; one second

Direct current (d.c.)

A current in which the carriers/electrons always travel in the same direction.

Alternating current (a.c.)

A current is which the charge carriers/electrons continually change their direction.

What is the relationship between power rating and resistance of an appliance for the same voltage?

The higher the power rating, the lower the resistance (P=V^2/R)

If the power rating of an appliance is less than 700W then a _____A fuse should be used.

3A

If the power rating of an appliance is equal to or more than 700W then a _____A fuse should be used.

13A