Page 60 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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1.4.14.2 Example 2
If a heater blower circuit has a 2 Ω and a 3 Ω resistor connected in parallel by the
speed control switch, what is the combined resistance?
The formula is /:1 R / 1 R / 1 R
T 1 2
Which means /1 R / 1 2 / 1 3
T
To add fractions the bottom numbers must be the same:
1/R 3 6/ 2 6/
T
1/R 5 6/ R 6 5/ .
1 2Ω
T T
1.4.15 Ratios
1.4.15.1 Example
2.5 1.0
If the maximum speed an alternator can run at is 15 000 r.p.m. and the top speed
of the engine is 6000 r.p.m., why is the pulley ratio 2.5:1? (Fig. 1.62)
15000 6000/ 2 5 the ratio of the speeds. ( ) 2.5 : 1

Therefore, the alternator can never be driven too fast. Figure 1.62 Pulley ratio

1.4.16 Areas
1.4.16.1 Example
1.2 m
If the car roof is 1.2 m long and 1.1 m wide and the aerosol says it will cover
2
1.5 m , will there be enough paint? (Fig. 1.63)
2
The area is 12. 11. 132. m
1.1 m
So yes, you have got enough paint (for one coat)!
Figure 1.63 Car roof
1.4.17 Volumes
Bore
1.4.17.1 Example 8 cm

If the bore of a four-cylinder engine is 8 cm and the stroke (distance from bottom
dead centre to top dead centre) is 6.9 cm, what is the capacity of the engine?
(Fig. 1.64) Stroke 6.9 cm
The volume of a regular solid is the area multiplied by the height. For a cylinder,
2
2
the area is π r , so the volume must be π r h ( r , the radius, is half the bore
diameter; h is the stroke):
Figure 1.64 Cylinder
V 3 14. 4 4 6 9. 346 66. ( now 4 cylinders ) 1386 62. cc

This engine would be called a 1400 cc or a 1.4 litre engine.
1.4.18 Indices

1.4.18.1 Example
A current fl ow of 1 ampere means that 6 000 000 000 000 000 000 electrons pass a
18
point in one second! It is much easier to write 6 10 , this simply means 6 with
18 zeros after it.
This quantity of electrons is known as a coulomb. It is about enough electricity to
work a heavy-duty starter motor for about 0.001 seconds. This could be written
3
as 10 seconds, where the 3 means moving the decimal point 3 places to the
left (dividing by 1000).