The question asks for the definition of extrusion. We need to identify the manufacturing process that correctly describes extrusion from the given options.
Correct Option: C) Pushing the heated billet of metal through the orifice
The question asks for the term used for a third flask placed between the cope and drag in a sand molding process. This relates to the terminology of multi-part molds used in casting.
D) Cheek is the correct term for a third flask used between the cope and drag in sand molding, especially for complex patterns.
The question asks for the primary method used in mass production of gears. We need to identify the manufacturing process that is most efficient and suitable for high-volume gear manufacturing.
C) Hobbing is a continuous generating process that is highly efficient and precise, making it the preferred method for mass production of gears, especially spur and helical gears.
The question asks to identify what "scab" refers to in the context of manufacturing defects. This requires knowledge of common defects associated with various manufacturing processes.
A) Sand casting defect
The following symbol depicts 
The given symbol needs to be identified among the options provided. Understanding the standard symbols used in electrical diagrams is crucial for this task.
Correct Option: C) Fuse
The question asks about the operating principle of a thermal relay. We need to identify the physical phenomenon that causes a thermal relay to function.
Correct Option: A) Heating effect of current. Thermal relays utilize the heat generated by an overcurrent to trip a protective mechanism, directly applying the heating effect of current.
The question asks to identify the component that is NOT a part of a DC machine. We need to recall the basic construction and working principles of a DC machine (both motor and generator) and identify its essential components.
A) Stabilizer — A stabilizer is an external device used to regulate voltage and is not an integral part of the internal construction or operation of a DC machine. DC machines have internal components like the stator, armature, and commutator for their fundamental operation.
The question asks about the type of transformer typically used in a voltage stabilizer. We need to identify the transformer type best suited for voltage regulation applications, considering its characteristics and common usage.
B) Auto Transformer — An auto transformer is commonly used in voltage stabilizers because it allows for continuous or stepped voltage regulation. It has a single winding with taps, enabling it to function as both a step-up and step-down transformer, making it ideal for correcting voltage fluctuations. They are more efficient and smaller for a given power rating when the voltage ratio is close to unity, which is often the case in stabilizers.
The question asks to identify the safety relay used in a transformer. This requires knowledge of common protective devices in power transformers and their functions.
Correct Option: C) Buchholz Relay is a gas-actuated relay specifically designed to detect internal faults in oil-immersed transformers, acting as a crucial safety device.
To determine the slip of an induction motor at synchronous speed, we need to recall the definition of slip and the conditions under which synchronous speed is achieved by the rotor.
Correct Option: A) zero