PHEP 25

Question 1

A DC meter may be compared to an electric _____

a) motor
b) generator
c) battery
d) rectifier

Answer 1

a) motor

Question 2

In a D’Arsonval type meter, the primary purpose of the iron core is to:

a) dampen the coil movement
b) concentrate flux between the core and pole piece
c) concentrate flux between the core and hair springs
d) weaken flux between the core and pole piece

Answer 2

b) concentrate the flux between the core and pole pieces

Question 3

The D’Arsonval movement operates on the principal of:

a) mutual induction
b) magnetic attraction
c) repulsion
d) magnetic repulsion and attraction

Answer 3

d) magnetic repulsion and attraction

Question 4

In most D’Arsonval movements, damping is accomplished automatically without the necessity for attaching some form of air vane and container to the mechanism. This is:

a) untrue because all meters use the air vane for damping purposes
b) true because one of the purposes of hairsprings is to provide damping
c) true because oscillation of the moveable coil (or bobbin) creates induced currents in the coil which opposes the motion
d) true because all of the energy of the moving element is absorbed by the action of the magnetic attraction

Answer 4

c) true because oscillation of the moveable coil (or bobbin) creates induced currents in the coil which opposes the motion

Question 5

A zero adjustment screw is provided on most Dc meters in order to adjust the:

a) range of the meter
b) sensitivity of the meter
c) pointer to the zero setting should it be off point
d) damping effect

Answer 5

c) pointer to the zero setting should it be off point

Question 6

The graduations of the calibrated scale on a D’Arsonval meter are uniform. This is because the degree of armature rotation is:

a) inversely proportional to the current
b) proportional to the cube of the current
c) proportional to the square of the current
d) directly proportional to the current

Answer 6

d) directly proportional to the current

Question 7

In a DC wattmeter, the two current coil and single voltage coil are so connected that

a) the voltage coil is in parallel to the line, and the current coils are in series with each other the and the line
b) all coils are in parallel
c) all coils are in series
d) the voltage coil is in series with the line, and the current coils in parallel with each other and the line

Answer 7

a) the voltage coil is in parallel to the line, and the current coils are in series with each other the and the line

Question 8

Before using an ohmmeter, the leads should be shorted together and the variable resistance knob adjusted so that the meter reads:

a) infinity
b) zero ohms
c) at a point midway between zero and infinity
d) at the base setting of the meter, usually 100 ohms

Answer 8

b) zero ohms

Question 9

A shunt is connect in parallel with the coil of a DC ammeter to permit the meter to measure larger amounts of current than the meter coil could safely carry. This statement is:

a) untrue because the shunts are connected in series with cell
b) true because the current being measured is caused to divide itself between the coil and the resistor
c) untrue because multipliers rather than shunts are used for this purpose
d) true because the shunt allows only 25% of the current being measured to pass through the meter coil.

Answer 9

b) true because the current being measured is caused to divide itself between the coil and the resistor

Question 10

When hair springs are used in D’Arsonval type meter, they:

a) serve as conductors
b) are wound oppositely and provide restoring forces
c) are attached to the ends of the bobbin
d) all above

Answer 10

d) all above

Question 11

Current measuring instruments must always be connected in:

a) series with a circuit
b) parallel with a circuit
c) series-parallel with a circuit
d) delta with the shunt

Answer 11

a) series with a circuit

Question 12

What 2 conditions may be observed in a Bridge circuit?

a) T and L network characteristics
b) no-load and full-load Bridge current
c) unequal potential and unequal current
d) balance and unbalance

Answer 12

d) balance and unbalance

Question 13

When first using a multi-range DC voltmeter on a circuit of unknown voltage, set the range selector at:

a) lowest point and work upward
b) highest point and work downward
c) any point. meters adjust itself automatically
d) the midway point between lowest and highest

Answer 13

b) highest point and work downward.

Question 14

With an ohmmeter setting on the Rx1 scale, it takes 0.01 milliamperes to deflect the pointer to half scale. If the meter was set on the Rx100 scale, how much current would it take to deflect the pointer to half scale?

a) 0.1 mA
b) 0.01 mA
c) 0.001 mA
d) 1.0 mA

Answer 14

b) 0.01 mA

Question 15

The ratings of four voltmeters are shown below. Which one would have the greatest sensitivity?

a) 100 ohms/volt
b) 1000 ohms/volt
c) 2000 ohms/volt
d) 100,000 ohms/volt

Answer 15

d) 100,000 ohms/volt

Question 16

The max current normally carried in a particular circuit is 150 amps. The DC ammeter best adapted to this circuit from the standpoint of safe efficient operation should have a range of:

a) 0-100 amps
b) 0-150 amps
c) 0-300 amps
d) 0-600 amps

Answer 16

c) 0-300 amps

Question 17

The least amount of meter error could be expected from an ohmmeter reading obtained from:

a) max deflection area of the pointer
b) min deflection area of the pointer
c) error value is the same throughout entire scale range
d) by using the lowest range or multiplication scale provided in the meter circuit

Answer 17

a) max deflection area of the pointer

Question 18

A meter is said to have good deflection torque characteristics when:

a) the hairsprings stop pointer oscillations in the minimum amount of time
b) the pointer rapidly hits zero when current flow stops
c) meter responds promptly to changes in measured force
d) all above

Answer 18

c) meter responds promptly to changes in measured force

Question 19

When using a DC voltmeter:

a) always connect the meter in parallel
b) start with range large enough to insure less than full-scale deflection
c) observe proper polarity
d) all above

Answer 19

d) all above

Question 20

In the Wheatstone Bridge type circuit on the next page the bridge current is toward point A. The resistance Rx is:

a) 30 Ohms
b) 45 Ohms
c) 20 Ohms
d) 15 Ohms

Answer 20

b) 45 Ohms