Page 155 - Physics Form 5 KSSM_Neat

Factors Affecting the Speed of Rotation of an CHAPTER 4
Electric Motor
Photograph 4.2 shows a portable device that can function as a
screwdriver or a drill. The direct current motor in the device Electromagnetism
rotates at a low speed when turning a screw. A high speed is
necessary when the device is used to drill a hole in the wall.
KEMENTERIAN PENDIDIKAN MALAYSIA
What are the factors that affect the speed of rotation of an
electric motor?
Photograph 4.2
Screwdriver and drill

Activity 4.6

Aim: To study the factors that affect the speed of rotation of an electric motor
Apparatus: Direct current power supply and a pair of Magnadur magnets
Materials: Insulated copper wire (s.w.g. 26), two large paper clips, two pieces of thumb tacks and
connecting wires
Instructions:
1. Set up the arrangement of apparatus as shown in Figure 4.14.
D.C. power supply

Copper wire coil
Large paper clip
AC + DC –

Magnadur
magnet

Thumb tack Connecting wire
Figure 4.14
2. Adjust the voltage of the power supply to 4.0 V. Turn on the Safety Precaution
Safety Precaution
power supply and observe the speed of rotation of the motor.
3. Repeat step 2 using a voltage of 6.0 V. • Switch off the power supply
immediately after an observation
4. Add one more Magnadur magnet to produce a stronger has been made.
magnetic field. Turn on the power supply and observe the • Current should flow for only a
speed of rotation of the motor. short time so that the coil will not
5. Add more turns to the copper coil. Turn on the power supply become too hot.
and observe the speed of rotation of the motor.
Discussion:
SCAN ME
1. What is the relationship between the current in the coil and the SCAN ME
voltage supplied? Video of rotation
of an electric
2. Describe the change in the speed of rotation of the motor when: motor
(a) the voltage supplied is increased
(b) the strength of the magnetic field is increased http://bit.ly/32imlPr
(c) the number of turns of the coil is increased
3. State the factors that affect the speed of rotation of a motor.

LS 4.1.6 145