12.1 Flashcards
Electric charge and current.
When do we say there is electric current in a conductor?
Similarly, if the electric charge flows through a conductor (for example, through a metallic wire), we say that there is an electric current in the conductor.
In a torch, what provides the charge that makes the torch glow?
In a torch, we know that the cells (or a battery, when placed in proper order) provide flow of charges or an electric current through the torch bulb to glow.
What does a switch do?
A switch makes a conducting link between the cell and the bulb.
Define electric circuit.
A continuous and closed path of an electric current is called an electric circuit.
How do we express electric current?
Electric current is expressed by the amount of charge flowing through a particular area in unit time. It is basically the rate of flow of charges through a conductor.
Direction of current.
Electric current was considered to be the flow of positive charges and the direction of flow of positive charges was taken to be the
direction of electric current. Conventionally, in an electric circuit the direction of electric current is taken as opposite to the direction of the flow of electrons, which are negative charges.
Current definition.
If a net charge Q, flows across any cross section of a conductor in time t, then the current I, through the cross-section I=Q/t.
Current formula.
I (current) = Q (charge) / t (time in seconds)
Charge and its SI unit.
The SI unit of electric charge is coulomb (C), which is equivalent to the charge contained in nearly 6.25 × 10^18 electrons.
Define charge.
It is a property of matter to attract or repel other materials. It is denoted by Q and its SI unit is Coulomb (C).
Charge in electron and proton.
1.6 * 10^-19 C > -ve charge in electrons.
1.6 * 10^-19 C > +ve charge in protons.
Define current.
Current is the amount of charge flowing through a particular area in unit time. It is the rate of flow of charges. If a charge Q flowed through a cross section in time t then current I would be = Q/t.
Current SI unit.
The SI unit of current is Ampere.
1 Ampere = 1Coulomb/1 second
1 A = 1 C / 1 s
Milliampere and Microampere.
milliampere = 1 mA = 10^–3 A
microampere = 1 μA = 10^–6 A
What is an ammeter? What device measures current?
An instrument called ammeter measures electric current in a circuit. It is always connected in series in a circuit through which the current is to be measured.
Schematic diagram of a circuit.
_____________M_______________
| |
| |
^ A
| |
|___|I|I|I _________<___(.)____|
M is bulb
|I|I|I is battery
(.) is a plug key
A is ammeter.
what direction does current flow?
Note that the electric current flows in the circuit from the positive terminal of the cell to the negative terminal of the cell through the bulb and ammeter.
A current of 0.5 A is drawn by a filament of an electric bulb for 10 minutes. Find the amount of electric charge that flows through the circuit.
We are given, I = 0.5 A; t = 10 min = 600 s.
From eq. we have
I= Q/t
so, Q = It
=> Q = 0.5 A × 600 s
=> Q = 300 C
What does an electric circuit mean?
An electric circuit is a closed continuous path of electric current.
Define the unit of current.
The SI unit of current is Ampere.
1 Ampere is the amount of current when 1 Coulomb of charge flows through a conductor in one second.
Calculate the number of electrons constituting one coulomb of charge.
6.25 * 10^18 electrons constitute one coulomb of charge.
