Thursday, 6 December 2012


Sources of electricity

Dry cells



 Solar cells

Rechargeable batteries 
Two types of circuits

 Series circuit

When the number of bulbs increases, the brightness of each bulb decreases. 
If any part of the circuit is broken, all bulbs do not light up.

 Parallel circuit

The number of bulb does not affect the brightness of each bulb. 
If one of the circuits is broken, the bulb in the other circuit still lights up.

Wednesday, 5 December 2012


 Circuits and Electricity

Multiple choices

1.  * Uses chemical energy to produce electricity
     * Produces a small amount of electricity
     * Suitable for toys, watches and torches

     The above description refers to ___________.
     A. an accumulator     B. a dry cell     C. a dynamo     D. a solar cell

2 . 

                                                         Diagram 1
 What is true about the objects shown in Diagram 1?
     A. They give us light.
     B. They possess kinetic energy.
     C. They are electric appliances.
     D. They are electrical energy sources.

3. * Converts energy from the Sun
    * used in calculators, watches and satellites

     What fits the description above?
     A. A dynamo     B. An accumulator     C. A solar cell     D. A dry cell

4.  What is the symbol for bulb?



5. Which of these actions should be avoided if someone gets electrocuted?
     A. Switch off the electricity supply.
     B. Pull the victim with your bare hands.
     C. Wear rubber gloves when handling the victim.
     D. Call an ambulance immediately.

1.B     2.D     3.C     4.B     5.B


1. All forms of energy including electrical energy cannot be created.
2. Dry cells and dynamos only convert one form of energy to another.
    For example, a dynamo converts kinetic energy to electrical energy.
3. All lights and electric appliances in houses are connected in parallel.
    They are controlled through their individual switches.
    If any one light or electric appliances is faulty, the rest are still able to function.

4. In a series circuit:
  • Each bulb is connected to another bulb in series.
  • The bulbs and switches are connected from one end of the circuit to the other.
  • Electricity flows along one path.
  • One switch controls all bulbs in the circuit.

5. in a parallel circuit:
  • The bulbs and switches are connected in parallel.
  • Each component is individually connected to the electric source.
  • Electricity flows along more than one path.
  • One switch controls only one path.


Accidents due to mishandling of electric appliances

1. Electricity is used almost everywhere in our lives.
    Almost all electric appliances in homes, schools, and offices use electricity to function.
2. Mishandling or careless use of electric appliances can cause electric shocks, fires,
    electrocutions and burns.

           electrocutions                                                                 burns

                                            electric shocks                                              fires

3. We should take safety precautions when using electric appliances.

Safety precautions

               Do not use faulty electric appliances.  Do not overload electric sockets.

 Do not run an extension lead into a bathroom.

 Do not insert any sharp objects into a socket.

Do not join an extra wire to make it longer.

Mishandling Electrical Appliances

Electrical Safety Tips


1. What is the effect on the bulbs when the various switches are turned on or off?

    (a) When the switches in a series and a parallel circuits are closed,
          the bulbs light up because the circuit are complete.
Series circuit

Parallel circuit
    (b) If a series circuit has more than one switch, all the bulbs do not light up
          if any one switch is open.

When switch P is closed and switch Q is open, bulbs R and S do not light up.

When switch P is open and switch Q is closed, bulbs R and S do not light up.

    (c) In a parallel circuit, each bulb is connected to its own switch.
         When one of the switches is open, only  the bulb connected to
         this switch will not light up. The other bulbs will still light up.

When switch W is closed and switch X is open, bulb Y lights up and bulb Z does not light up.

When switch W is open and switch X is closed, bulb Y does not light up and bulb Z lights up.


C) Brightness of bulbs connected in a series and parallel circuits

To compare the brightness of bulbs connected in a series and parallel circuits

How does the type of circuit used affects the brightness of bulbs?
  • What to change: The type of circuit
  • What to observe: The brightness of the bulbs
  • What to keep the same: The number and type of bulbs and dry cells
Circuit R

Circuit S
1. Two bulbs are connected
    (a) in series as in circuit R
    (b) in parallel as in circuit S
2. The switches in both circuit are closed at the same time.
    The brightness of the bulbs in circuits R and S are compared.


Brightness of bulbs

The bulbs in parallel in a circuit shine brighter than the bulbs in a series circuit if similar bulbs and dry cells are used.


B. Brightness of bulbs in a parallel circuit

To compare the brightness of bulbs in a parallel circuit

Is the brightness of bulbs in a parallel circuit affected by its number?
  • What to change: The number of bulbs
  • What to observe: The brightness of the bulbs
  • What to keep the same: The type and number of dry cells, and The type of bulbs

1. Two similar parallel circuits are connected as shown in the diagram.
2. Circuit P has two bulbs while circuit Q has three bulbs.
3. Both circuits are switched on and the brightness of the bulbs is observed.


Brightness of bulb
P (with two bulbs)
Both bulbs shine with similar brightness.
Q ( with three bulbs)
All the bulbs shine with similar brightness as in P

The brightness of bulbs remains the same when the number of bulbs in a parallel circuit is changed.