Standard symbol for light-dependent resistor (LDR)

Steps:

• Identify LDR as a resistor whose resistance decreases with light intensity.
• Recall standard circuit symbol: a resistor (zigzag line) with two inward arrows representing light rays.
• Examine choices for the symbol matching this description.
• Select the option showing resistor with light-indicating arrows.

Why D is correct:

• D depicts the conventional LDR symbol, where arrows indicate light sensitivity, per IEC 60617 standards.

Why the others are wrong:

• A is the fixed resistor symbol (zigzag line only), lacking light indication.
• B is the variable resistor symbol (with adjustment arrow), not for light dependence.
• C is the thermistor symbol (with temperature mark), for heat sensitivity, not light.

Final answer: D