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Flashcards in Electricity 5 Of 7 Deck (34)
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1

What are the four basic meters?

1-ammeter
2-voltmeter
3-ohmmeter
4-wattmeter

2

Can a current meter be calibrated in units other that amps?

Yes, in can be calibrated in voltage and resistance because all three are related to ohms law

3

When current flows through a wire, it produces what two effects?

1-it creates a magnetic field around the wire.
2- it generates heat

4

The _________ current meter makes use of the magnetic field around a current-carrying wire to measure current.

Electromagnetic

5

The ___________ meter uses the heat produced by a wire to measure current.

Thermal

6

The __________ of the magnetic field is proportional to the amount of ______________ flowing through the coil.

Strength
Current

7

What are the two types of electromagnetic current meters?

1) moving-coil type
2) moving-iron type

8

The first known moving-coil meter was called?

Galvanometer

9

Because it is very accurate and rugged, the _______________ is the most common meter used

Moving-coil movement

10

What are the three types of moving-iron meters?

1) radial vane
2) concentric-vane, and
3) plunger type

11

When current flows through a wire, the wire is heated_________ to the current flow.

Proportionally

12

In the concentric-vane meter, the stationary vane is ______ to provide a nonuniform magnetic field between the two vanes.

Tapered.

13

What are the typical three shapes of pointers?

Spade
Knife
Lance

14

The ___________ meter movement is used most often because it is more sensitive and more accurate.

Moving-coil

15

By using a _________ to convert ac to dc, moving-coil meters can be used in a-c applications.

Rectifier

16

To calibrate a d-c meter, an ___________ d-c current source is connected.

Accurate.

17

The d-c current source used to calibrate a d-c meter must be very accurate and?

Be variable and have a means to monitor the output current.

18

The accuracy of a meter is the percentage error at ____________ deflection.

Full-scale

19

What type of special resistor is used in amp meters?

A shunt.

20

Meters designed to measure currents above 30 amps generally use _________ shunts.

External

21

A rectifier changes a sine wave into a __________ d-c wave.

Pulsating

22

What are the two types of rectifiers?

Full wave and half wave

23

What is used in a full-wave rectifier to allow current to flow in the same direction during both alternations of a sine wave?

Bridge rectifier circuit

24

__________ rectifiers measure only one half the alternation of a sine wave.

Half-wave

25

A________ is used to select a particular shunt for the desired current range.

Range switch

26

A current meter must always be connected in __________ with the power source and load.

Series

27

Do you have to observe the polarity when connection a meter to ac?

No, because the polarity changes with each alternation

28

A clamp-on meter acts like a _________ because current through the conductor produces a magnetic field which induces current.

Transformer

29

The closer a pointer is to __________________ the more accurate it is.

Full-scale deflection

30

The voltage range of a meter can be extended by adding a _______ in series.

Multiplier resister