Understanding Submarine Speed Measurement in Deep Sea

The question asks about suitable instruments for measuring the speed of a submarine when it is moving in the deep sea. Let's examine the provided options:

• Venturi meter: A Venturi meter is a device used to measure the flow rate of a fluid in a pipe. It works by reducing the cross-sectional area of the flow path, causing a pressure difference that is proportional to the flow rate. This instrument is designed for use within closed conduits and measures fluid flow, not the speed of a large object like a submarine moving through an open body of water like the deep sea. Therefore, a Venturi meter is not suitable for measuring submarine speed.
• Orifice plate: Similar to a Venturi meter, an orifice plate is used to measure the flow rate of a fluid by creating a pressure drop as the fluid passes through a restricted opening (the orifice). Like the Venturi meter, it is designed for flow measurement in pipes and is not applicable to determining the speed of a submarine in the deep sea.
• Hot wire anemometer: A hot wire anemometer is primarily used for measuring the speed of air or gas flow. It works by sensing the cooling effect of the fluid flow on a heated wire; the faster the flow, the more the wire cools, changing its electrical resistance. This instrument is not designed for use in water, especially the high pressures and specific conditions encountered in deep sea environments. It is certainly not suitable for measuring the speed of a submarine.

None of the instruments listed—Venturi meter, Orifice plate, or Hot wire anemometer—are appropriate for measuring the speed of a submarine moving in deep sea. Submarines typically use specialized systems for speed measurement, such as Doppler Velocity Logs (DVLs), which use acoustic signals bounced off the seabed or water layers, or sophisticated Inertial Navigation Systems (INS) that track movement using gyroscopes and accelerometers.

Since none of the provided options are suitable instruments for measuring the speed of a submarine in deep sea, the correct choice is that none of these instruments can be used for this purpose.