Ampere

This article discusses Ampere – the unit of electric current, in detail. Ampere is the unit that we use to quantify the current flowing in a system. An ampere is equivalent to a charge of one Coulomb per second.

What is Ampere?

• Ampere is named after the French Physicist and Mathematician Andre-Marie Ampere. 
• One ampere of current represents one coulomb of electrical charge, i.e. 6.24×1018 charge carriers, moving in one second. 
• In other words, “an ampere is the amount of current produced by the force of one volt acting through a resistance of one ohm”.

• Ampere is defined as the unit of electric current that is equal to the flow of one Coulomb per second.
• The relationship between ampere and coulomb is represented as follows:
• Ampere = 1 Coulomb / Second
• At any given point in an area experiencing current, the Ampere value will increase proportionately if the charge on particles moving through it increases.

Table of Ampere Unit Prefixes

• A huge range of electric current values is encountered in electrical and electronic engineering. 
• An electric current value can be lower than 0.01 A or higher than 1000 A. 
• By using multiples and submultiples of the standard unit we can avoid writing too many zeroes to define the position of the decimal point. 
• The table below lists some of the commonly used ampere unit prefixes.

Name	Symbol	Conversion	Example
microampere(microamps)	μA	1 μA = 10-6A	I = 40 μA = 40 × 10-6A
milliampere(milliamps)	mA	1 mA = 10-3A	I = 2 mA = 2 × 10-3 A
ampere (amps)	A	–	I = 20 A
kiloampere(kiloamps)	kA	1 kA = 103A	I = 4 kA = 4 × 103 A

Ampere Conversion

Unit conversion is crucial in solving problems. Below we have listed examples of ampere conversions from one scale to another.

Conversion of amps (A) to kiloamps(kA)

One kiloamp (kA) equals a thousand amps (A).

1 kA = 1000 A or 1 × 103  A

For example, 5 amperes of current can be converted to kiloamperes as follows:

5 A × 1000 = 5000 A or 5 kA

Conversion amps (A) to milliamps (mA)

One milliampere is equal to 1000 amperes.

1 mA = 1000 A

For example, 2 A to milliampere is converted as follows:

2 A/1000 = 0.002 A or 2 × 10-3 A = 2 mA

Conversion of amps (A) to microamps (μA)

One Ampere is equal to 1000000 or 10-6 microamperes.

1 μA = 1000000 A

For example, 5 A is converted to microamps as follows:

5 A / 1000000  = 0.000005 A or 5 × 10-6  A = 5 μA

Conversion of Watt, Volt and Ohm into Ampere

The electric current value can be calculated by knowing the voltage, power and resistance values.

Calculation of Amps with Watts and Volts

• The power of the circuit is given by the following formula:
• P (Watt) = V (Volt) × I (Ampere)
• Rearranging the above equation, we can calculate the value of electric current as follows:
• I (Ampere) = P (Watt) / V (Volt)

Solved Example:

What is the current flow in a circuit that consumes 50 W of power and has a supply voltage of 10 V?

Using the equation, we can calculate the current as follows:

I (A) = 50 W/10 V = 5 A

Calculation of Amps with Volts and Ohms

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• The resistance of a circuit is calculated using the following formula:
• V (Volt) = I (Ampere) × R (Ohm)
• Rearranging the above formula, we can calculate the value of electric current as follows:
• I (Ampere) = V (Volt) / R (Ohm)

Solved Example:

What is the current in a circuit having a voltage of 25 V with a resistance of 5 Ω?

Using the above equation, we can calculate the value of the current as follows:

I = 25 V/5 Ω = 5 A

Ampere Meter/Ammeter

Ampere meter, commonly known as Ammeter is an electrical instrument used to measure electrical current in Amperes. The electrical current on the load is measured with the help of an Ampere meter by connecting it in series to the load. It has zero resistance, and so the measured circuit remains unaffected.

What happens when an ammeter is connected in parallel to load?

• The ammeter cannot be connected in parallel to the load because of its low resistance. 
• If it is connected in parallel, it becomes a short circuit path allowing all the current to flow through it which may lead to the burning of the metre due to the high current value. 
• An ideal ammeter has zero impedance, so the instrument’s power loss is zero. 
• But this ideal condition is not achievable practically.

Types of Ammeter

The classification of the ammeter is based on the construction design and the type of current that flows through the ammeter.
Based on the design of construction it is classified as follows:

• Moving iron ammeter
• Rectifier type ammeter
• Permanent moving coil ammeter
• Electro-dynamometer ammeter

Based on the type of current that flows through it, it is classified as follows:

• DC ammeter
• AC ammeter

The DC ammeters are mostly permanent moving coil type ammeter. The other types of ammeter can measure both AC and DC current.

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