Ammeter Practice Questions
19 free Ammeter practice questions for the General Science. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
What is the primary function of an ammeter in an electrical circuit?
- A To measure the potential difference between two points
- B To measure the rate of flow of electric current
- C To measure the resistance of a conductor
- D To increase the voltage of the power source
Correct answer: To measure the rate of flow of electric current
An ammeter is designed to measure electric current in Amperes. It quantifies the amount of electric charge passing through a point in the circuit per unit of time.
How must an ammeter be connected in a circuit to correctly measure the current through a specific component?
- A In parallel with the component
- B In series with the component
- C Across the battery terminals
- D Between ground and chassis
Correct answer: In series with the component
To measure the flow of electrons, the ammeter must be part of the same path as the component. Connecting it in series ensures that the same current flowing through the component also passes through the meter.
An ideal ammeter is theorized to have which of the following properties?
- A Infinite internal resistance
- B Zero internal resistance
- C High voltage capacity
- D Thermal insulation
Correct answer: Zero internal resistance
An ideal ammeter has zero resistance so that it does not create a voltage drop or change the total resistance of the circuit. This ensures that the instrument's presence does not alter the current it is trying to measure.
What is the likely result of connecting an ammeter in parallel with a high-voltage power source?
- A The ammeter will show a very precise reading.
- B The circuit will become significantly more efficient.
- C The ammeter will short circuit and likely burn out.
- D The voltage of the source will increase sharply.
Correct answer: The ammeter will short circuit and likely burn out.
Because an ammeter has very low internal resistance, connecting it in parallel creates a low-resistance path for the current. This leads to a massive surge of current (a short circuit) that can destroy the meter and blow fuses.
Which component is used to extend the range of a DC ammeter?
- A A high resistance connected in series
- B A low resistance in parallel
- C A capacitor in series
- D An inductor in parallel
Correct answer: A low resistance in parallel
To measure currents larger than the meter's basic capacity, a 'shunt' resistor is connected in parallel. Most of the current flows through the shunt, while a small, proportional fraction flows through the sensitive meter movement.
Which type of ammeter is used to measure alternating current (AC) without the need for a rectifier?
- A Permanent Magnet Moving Coil (PMMC) ammeter
- B Moving Iron (MI) ammeter
- C Digital DC ammeter
- D Rectifier-type ammeter
Correct answer: Moving Iron (MI) ammeter
Moving Iron instruments respond to the square of the current, making them suitable for both AC and DC. They do not depend on the direction of the current, which is necessary for measuring alternating signals.
What does a 'Center-Zero' ammeter indicate?
- A The circuit being tested has zero resistance.
- B The meter is calibrated only for AC.
- C The meter is currently turned off.
- D The current can flow in either direction.
Correct answer: The current can flow in either direction.
A center-zero ammeter has the zero mark in the middle of the scale. This allows the needle to deflect left or right, indicating both the magnitude and the direction (polarity) of the current flow.
Which ammeter works on the principle of the heating effect of electric current?
- A PMMC ammeter
- B Electrostatic ammeter
- C Induction ammeter
- D Hot-wire ammeter
Correct answer: Hot-wire ammeter
In a hot-wire ammeter, current passes through a wire, causing it to heat up and expand. The expansion of the wire is mechanically linked to a pointer, providing a reading that is independent of wave shape or frequency.
What is the sensitivity of an ammeter defined as?
- A The maximum current the meter can safely measure
- B The resistance of the shunt resistor used
- C The weight of the moving coil assembly
- D The current needed for full-scale deflection
Correct answer: The current needed for full-scale deflection
Ammeter sensitivity is stated as the current required to drive the pointer to full-scale deflection. The smaller that current, the more sensitive the instrument.
In a digital ammeter, the current is measured by detecting the voltage drop across a:
- A Step-down current transformer
- B Semiconductor diode
- C Dielectric insulator
- D Known precision resistor
Correct answer: Known precision resistor
Digital ammeters typically pass the current through a high-precision internal shunt resistor. The resulting small voltage drop across this resistor is measured and converted by an analog-to-digital converter into a current reading.
Why is it important to check the 'polarity' when connecting a DC ammeter?
- A To prevent the meter's magnetic field from weakening.
- B To increase the internal resistance of the meter.
- C To prevent the wires from melting.
- D To ensure the needle deflects the correct way.
Correct answer: To ensure the needle deflects the correct way.
DC ammeters are polarized. If the positive and negative terminals are reversed, the needle will attempt to move backwards (below zero), which can bend the needle or damage the internal movement.
What is the SI unit of electric current measured by an ammeter?
- A Coulomb
- B Ohm
- C Ampere
- D Watt
Correct answer: Ampere
The Ampere (A) is the base SI unit for electric current. It represents the flow of one Coulomb of electric charge per second.
Which of the following is used to measure very small currents in the microampere range?
- A Milliammeter
- B Voltmeter
- C Wattmeter
- D Microammeter
Correct answer: Microammeter
A microammeter is a highly sensitive ammeter calibrated to measure currents in millionths of an Ampere (μA). It is commonly used in low-power electronic sensing and laboratory experiments.
What is the purpose of the 'clamping' mechanism on a Clamp-on Ammeter?
- A To clamp the meter's leads onto the conductor
- B To protect the meter from high-voltage arcing
- C To measure current without breaking the circuit
- D To increase the resistance of the wire being measured
Correct answer: To measure current without breaking the circuit
A clamp-on ammeter (or current clamp) measures the magnetic field generated by current flowing through a conductor. This allows the user to measure current without physically disconnecting the wire to insert the meter.
The internal resistance of a 'milliammeter' is usually __________ that of a standard ammeter.
- A Higher than
- B Lower than
- C The same as
- D Negligible compared to
Correct answer: Higher than
A milliammeter measures smaller currents and therefore has a higher internal resistance than a standard ammeter. A standard ammeter needs a lower resistance to handle larger current flows without overheating or affecting the circuit.
Which ammeter is most accurate for high-frequency radio current measurements?
- A Thermocouple ammeter
- B Moving Iron ammeter
- C PMMC ammeter
- D Electrodynamometer ammeter
Correct answer: Thermocouple ammeter
Thermocouple ammeters use the heat generated by the current to produce a voltage in a thermocouple junction. Because this process is based on heat, it is effective even at very high frequencies where magnetic meters fail.
What does a 'Full-Scale Deflection' (FSD) current of 10A mean for an ammeter?
- A The meter cannot measure any current below 10A.
- B The meter is most accurate at 10A.
- C 10A is the largest current the scale can show.
- D The meter has a resistance of 10 Ohms.
Correct answer: 10A is the largest current the scale can show.
FSD is the maximum value on the display scale. Attempting to measure a current higher than the FSD can 'peg' the needle against the stop pin, leading to mechanical damage.
Which of the following ammeters is used only for AC circuits and works on the principle of electromagnetic induction?
- A Moving Coil ammeter
- B Moving Iron ammeter
- C Induction ammeter
- D Hot-wire ammeter
Correct answer: Induction ammeter
Induction ammeters rely on the interaction between a fluctuating magnetic field and the currents it induces in a movable disk. Because induction requires a changing field, they cannot function with Direct Current (DC).
What is the function of the 'damping' mechanism in an analog ammeter?
- A To keep the needle from oscillating as it settles.
- B To cool the internal coil windings.
- C To increase the sensitivity of the meter.
- D To protect the meter from stray magnetic interference.
Correct answer: To keep the needle from oscillating as it settles.
Damping (usually eddy current or air damping) provides a counter-force to the needle's motion. This prevents the needle from swinging back and forth excessively, allowing for a faster and more stable reading.