A resistor with fixed resistance value is called a

Analyze the question: It asks for the name of a resistor whose resistance value is fixed (it does not change).

Explain the concept: Resistors are grouped by whether their value can change:

• Fixed resistors have a set resistance, such as carbon or wire-wound resistors. In a laboratory, a fixed resistor of accurately known value is called a standard resistor.
• Variable resistors include rheostats and potentiometers, and their resistance can be adjusted.
• A resistance box contains several resistors that can be switched in or out. It gives different values, so it is not fixed.
• A shunt resistor is a low-resistance resistor connected in parallel with a galvanometer to make an ammeter. It is named for its use, not for being fixed.
• A multiplier resistor is a high-resistance resistor connected in series with a galvanometer to make a voltmeter. It is also named for its use.

Step by step:

1. Option A, the resistance box, gives adjustable values, so it is eliminated.
2. Options C and D are names for resistors based on their role in meters (ammeter and voltmeter conversion), not on the property of being fixed. They are eliminated.
3. Option B, the standard resistor, is the term for a resistor with a fixed, known value.

Answer: B. standard resistor.

Exam tip: Remember the pairs:

• Shunt goes in parallel and makes an ammeter.
• Multiplier goes in series and makes a voltmeter.
• Fixed means standard, and adjustable means rheostat or resistance box.