Examiner's Expectation: 2.15 Students will be assessed during examination on their ability to understand that current is the rate of flow of charge

 

Examiner's Expectation: 2.16 Students will be assessed during examination on their ability to recall and use the relationship between charge, current and time:      charge = current × time      (Q = I × t)

 

We know that Charges are developed on objects through friction.

We also know that charges can move from one object to another and can also be spread out over a conductor.

When electric charges move from one place to another in a particular time, we call it an electric current.  Faster the charges move, greater would be the current.

The word "flow" is often associated against the "word" move in the definition of electric current. Therefore, the definition of electric current is Rate of Flow of Charges.

In metals, these moving charges are electrons, which carry negative charges.  1 electron carries 1.69 x 10-19 coulmbs or charges.

Following cylinder shows the flow of negative charges in a conductor

current in cylinder

Then the electric current "I" through the wire is

Current (I) = Charge (Q) / Time (t)

where, the unit of Charge is "Coulomb" and unit of time is "second". Therefore, unit of Current, which is Amperes (A) would be 1 A = 1 C / S

According to above equation, current is defined as flow of charges per second. Therefore, current can be increased by increasing the number of charges or increasing their speed (reducing time of flow.)

Try the following questions

 

Question#1

 

QITquestion

 

Question#2

 

QITquestion2