Introduction to Current

Electricity, Part 1Grade 9 Academic Science

R.H. King Academy

Recall

Static electricity is the build up of charges on surfaces

An object becomes positively charged by losing

electrons

An object becomes negatively charged by gaining

electrons

Current Electricity

Current electricity is the flow of electrons

This type of electricity is used to power all of your

electrical devices

How does current electricity work?

Watch this video (only up to 5:20)

http://www.youtube.com/watch?v=D2monVkCkX4

Video Questions

1. How does current electricity differ from static

electricity?

2. Identify the two terminals of a battery.

3. How does electricity flow from one terminal to the

other?

4. What will happen if you connect a short wire between

the two terminals of a battery?

5. The power (potential difference) in a battery or the

socket in the wall is measured in __________. An AA

battery is ________, and the wall socket is ___________.

Circuits Current electricity is the steady flow of electrons

from a negative terminal to a positive terminal in a

circuit

A circuit includes:

An energy source (e.g. battery)

A conductor (e.g. wire)

A load (e.g. light bulb)

A circuit may include:• A switch to turn the circuit on

and off

Optional Accessory: Switches

The electricity does not come from the switch!

A switch simply opens and closes a circuit.

When you open the circuit, electrons stop flowing. Electrical

devices turn off.

When you close the circuit, electrons can flow. Electrical

devices turn on.

Symbols

Wire

battery / cell

light bulb / lamp

Resistor

Switch

Ammeter

voltmeter

How to measure current

electricity

Three factors are measured in current electricity:

1.Potential difference: measured in volts (V)

2.Current: measured in amperes (A)

3.Resistance: measured in ohms (Ω)

Current

When electrons flow in a circuit, this is called current

There are two types of current:

1. Direct Current (DC): All the electrons flow in one direction. Batteries produce this type of current.

2. Alternating Current (AC). The electrons flow back and forth at regular intervals and cycles. This is the current that is produced by generators and is delivered to our electrical sockets

See the difference here:

http://kids.britannica.com/lm/animations/oaltern001d4/product.html

Current

To measure current, you measure the number of

electrons that are flowing through a circuit

This measurement is in amperes (A), also called amps

1 ampere = 1 coloumb of electrons passing by every

second

Therefore, 1 ampere = 6.24 x 1018 electrons passing by a

point in the circuit every second!

Ammeter An ammeter measures current in a circuit

What does 0.5 A mean?

Equations to know!

Q = Charge [C]

I = Current [A]

t = Time [s]

Q = I x t

I = Q/t

t = Q/I

Note: time is always measured

in seconds

Current Problems

Use GRASP to solve the following problems.

G: Given R: Required A: Analysis (formula) S: Solution P: Paraphrase

Calculate the current of a circuit that has a charge of 960 C flowing through it for a time of 25 min.

A circuit has a current of 2.50 A running through it. Calculate the total charge transferred in the circuit if it runs for a total of 45 s.

Calculate the time required for a circuit with a current of 1.75 A to transfer a total charge of 650 C.

A circuit transfers a total charge of 1450 C in a time of 75 min. What is the current of the circuit?

Homework

Pg 436 # 1-3

Handout questions on current