# 42 Lecture

## PHY101

### Midterm & Final Term Short Notes

## Special Relativity – I

Special relativity is a fundamental theory in physics that deals with the behavior of objects in motion relative to each other.

**Important Mcq's**

Midterm & Finalterm Prepration

Past papers included

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**Which of the following is not a postulate of special relativity?**

a) The laws of physics are the same in all inertial frames of reference

b) The speed of light in vacuum is the same in all inertial frames of reference

c) The laws of physics are the same in all non-inertial frames of reference

d) The principle of relativity

**Answer: c) The laws of physics are the same in all non-inertial frames of reference**

**According to special relativity, which of the following is not an absolute quantity?**

a) Energy

b) Momentum

c) Velocity

d) Mass

**Answer: c) Velocity**

**In special relativity, the factor that relates time and space intervals between two events is known as:**

a) The speed of light

b) The Lorentz factor

c) The Doppler effect

d) The Michelson-Morley factor

**Answer: b) The Lorentz factor**

**What is the proper length of an object?**

a) The length of the object measured in its rest frame

b) The length of the object measured in a moving frame of reference

c) The length of the object measured by an observer at rest relative to the object

d) The length of the object measured by an observer moving with the object

**Answer: a) The length of the object measured in its rest frame**

**Which of the following statements is true regarding time dilation in special relativity?**

a) Time dilation occurs only for objects moving at speeds close to the speed of light

b) Time dilation occurs for all objects in motion

c) Time dilation occurs only for objects at rest

d) Time dilation occurs only for objects in free fall

**Answer: b) Time dilation occurs for all objects in motion**

**According to special relativity, the faster an object moves:**

a) The slower its internal clocks run

b) The faster its internal clocks run

c) Its internal clocks do not change

d) None of the above

**Answer: a) The slower its internal clocks run**

**In special relativity, the principle of causality is maintained by:**

a) The relativity of simultaneity

b) The equivalence principle

c) The principle of least action

d) The principle of locality

**Answer: a) The relativity of simultaneity**

**The twin paradox in special relativity involves:**

a) Two twins who travel at different speeds and reunite to find that one has aged more than the other

b) Two twins who travel in opposite directions and reunite to find that they have aged the same amount

c) Two twins who travel at the same speed and age at the same rate

d) None of the above

**Answer: a) Two twins who travel at different speeds and reunite to find that one has aged more than the other**

**According to special relativity, the mass of an object:**

a) Increases as its velocity increases

b) Decreases as its velocity increases

c) Remains constant regardless of its velocity

d) None of the above

**Answer: b) Decreases as its velocity increases**

**The formula E=mc² in special relativity relates:**

a) Energy and momentum

b) Energy and mass

c) Mass and momentum

d) None of the above

**Answer: b) Energy and mass**

**Subjective Short Notes**

Midterm & Finalterm Prepration

Past papers included

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**What is the principle of relativity?**

**Answer: **The principle of relativity states that the laws of physics are the same for all observers in uniform motion relative to one another.

**What is the difference between Galilean relativity and special relativity?**

**Answer:** Galilean relativity is based on the principle of relativity, but it does not take into account the constant speed of light. Special relativity includes the constant speed of light as a fundamental aspect of the theory.

**What is time dilation?**

**Answer:** Time dilation is the effect that occurs when the time interval between two events is perceived to be different by two observers who are moving relative to one another.

**How does time dilation arise in special relativity?**

**Answer: **Time dilation arises from the fact that the speed of light is always constant, regardless of the motion of the observer. As a result, time appears to be slower for a moving observer than for a stationary observer.

**What is the twin paradox?**

**Answer: **The twin paradox is a thought experiment that involves two identical twins, one of whom travels at high speed in space while the other stays on Earth. When the space-traveling twin returns, he or she will have aged less than the twin who stayed on Earth.

**What is length contraction?**

**Answer:** Length contraction is the effect that occurs when the length of an object is perceived to be shorter in the direction of motion by an observer who is moving relative to the object.

**What is the Lorentz factor?**

**Answer**: The Lorentz factor is a quantity that appears in special relativity and is defined as 1/sqrt(1-v^2/c^2), where v is the velocity of an object and c is the speed of light.

**How does the concept of simultaneity change in special relativity?**

**Answer: **In special relativity, the concept of simultaneity is relative to the observer's frame of reference. Two events that are simultaneous in one frame of reference may not be simultaneous in another frame of reference.

**What is the energy-momentum relationship in special relativity?**

**Answer:** The energy-momentum relationship in special relativity is given by the equation E^2 = (pc)^2 + (mc^2)^2, where E is the energy of a particle, p is its momentum, m is its mass, and c is the speed of light.

**What is the significance of the speed of light in special relativity?**

**Answer: **The speed of light is a fundamental constant in special relativity and plays a crucial role in determining the behavior of objects moving at high speeds. It is the ultimate speed limit in the universe, and nothing can travel faster than it.