Ch.8.3 Flashcards
What is matter made up of?
Atoms.
Describe the structure of atoms.
Each atom has a nucleus surrounded by tiny electrons.
The nucleus of an atom carries a __________________ charge, while electrons carry a __________________ charge.
positive, negative
What is the relationship between ions and atoms?
Ions are charged atoms — the neutral proton no. is not equal to the electron no.
Atoms are neutral — the neutral proton no. is equal to the electron no.
What are free electrons?
The electrons that can escape from the atoms and move freely within metals.
When a metal is connected to an electric cell to form a closed circuit, free electrons are driven to ______________________________________________________________________________________________________. This forms an _________________ _________________.
flow in a direction from the negative pole towards the positive pole of the electric cell
electric current
Before the discovery of electrons, scientists believed that an electric current was ______________________________________________________________________________________________________. This is called the _________________ _________________.
a flow of positive charges from the positive pole of the electric cell to the negative pole
conventional current
What are the directions of the flow of electrons in the concepts of electric currents and conventional currents respectively?
— ➞ +
+ ➞ —
Do scientists still use the conventional current?
Yes.
The size of an electric current is related to ________________________________________________________________________________________________________________.
the number of free electrons that flow through a point in the circuit every second
The _________________ free electrons flowing through a circuit, the _________________ the electric current.
more, larger
We can use an _________________ to measure the size of an electric current.
ammeter
What are the units of an electric current?
ampere (A) or smaller, milliamperes (mA)
1A=?mA
1000
An ammeter has a _________________ terminal (_________) and a _________________ terminal (_________).
positive, red, negative, black
How should be the ammeter connected?
It should be connected so that the electric current flows into the ammeter at its positive terminal and leaves from its negative terminal.
In the experiment of using an ammeter to measure an electric current, why do we have to add a light bulb to the circuit?
This is because the current will be too large and may damage the ammeter without the bulb.
The ________________ the current, the ________________ the brightness of a light bulb in a circuit.
larger, higher
When an electric current flows through a conductor, ________________________________________________________________________________. This is the ________________ ________________ of ________________ ________________.
(hint: related to energy conversion)
some of the electrical energy changes to thermal or even light energy
heating effect, electric current
The ________________ the electric current, the ________________ the heating effect.
larger, larger
The heating effect of electric current is ________________.
useful
Some ________________ ________________ such as electric kettles make use of the heating effect to work.
electrical appliances
Explain the use of a fuse.
When the temperature of an electrical appliance is higher than its conductors’ melting points, the fuse breaks to open the circuit, and hence protects the current from being too hot.
Besides heating effect, electric current also produces a ________________ ________________.
magnetic effect
How can we test for the magnetic effect of an electric current?
When an electric current flows through a wire or a coil, the needle on a compass nearby changes direction.
The ________________ the electric current, the ________________ the magnetic effect.
larger, larger
When an electric current flows through a coil, the coil can ________________ iron paper clips like a ________________. The coil is called an ___________________________.
attract, magnet, electromagnet
What are the pros of electromagnets?
—
—
the strength of the attraction can be controlled by the size of current
the magnetic effect can be switched on or off
Under what circumstances can electromagnets produce a magnetic effect?
When an electric current flows through it.
Electromagnets are commonly used in devices such as ________________ ________________ ________________, ________________ ________________ etc.
electric door locks, electric bells
