An electric device delivers a current of [tex]$15.0 A$[/tex] for 30 seconds. How many electrons flow through it?
Answer (2)
A current of 15.0 A for 30 seconds results in a total charge of 450 coulombs. Using the charge of an electron (approximately 1.6 x 10^-19 C), we find that approximately 2.81 x 10^21 electrons flow through the device. This demonstrates the relationship between current, charge, and the number of electrons in an electric circuit.
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Calculate electric power using P = V × I : P = 220 V × 5 A = 1100 W .
Uniform velocity means both magnitude and direction are constant.
Moment of force is a vector quantity.
The angle between magnetic and geographical meridians is the angle of declination.
If light bends away from the normal, the second medium is rarer.
C , A , D , B , B , A , A
Explanation
Problem Analysis Let's analyze each question step by step.
Question 69: We are given the voltage ( V ) and current ( I ) of an electric heater and asked to find its electric power ( P ). The formula for electric power is P = V I .
Question 70: We need to identify the correct statement about uniform velocity. Uniform velocity means that both the magnitude (speed) and direction of the velocity remain constant.
Question 71: We need to identify which of the given quantities is a vector quantity. A vector quantity has both magnitude and direction.
Question 72: We need to identify the unit of intensity of sound.
Question 73: We need to identify the instrument used to detect the flow of electric current in an electric circuit.
Question 74: We need to identify the angle between the magnetic meridian and the geographical meridian.
Question 75: We need to determine the relationship between the angle of refraction and the density of the medium when a ray of light enters from one medium to another.
Detailed Solutions Question 69: Given: V = 220 V and I = 5 A .
Using the formula P = V × I , we calculate the power: P = 220 V × 5 A = 1100 W Therefore, the electric power of the heater is 1100 watts.
Question 70: In uniform velocity, both magnitude and direction remain constant. So the correct answer is A.
Question 71:
Work is a scalar quantity (energy transferred).
Power is a scalar quantity (rate of energy transfer).
Speed is a scalar quantity (magnitude of velocity).
Moment of force (torque) is a vector quantity (force times distance, with direction).
Therefore, the vector quantity is moment of force.
Question 72: The unit of intensity of sound is decibel (dB).
Question 73: An ammeter is used to detect the flow of electric current in an electric circuit.
Question 74: The angle between the magnetic meridian and the geographical meridian at a place is known as the angle of declination.
Question 75: If a ray of light increases its angle with the normal when entering a new medium, it means the light is bending away from the normal. This happens when light enters a rarer medium. Therefore, the second medium must be rarer than the first medium.
Final Answers Question 69: The electric power is 1100 watt. The correct option is C. Question 70: In uniform velocity, both magnitude and direction remain constant. The correct option is A. Question 71: The vector quantity is moment of force. The correct option is D. Question 72: The unit of intensity of sound is dB. The correct option is B. Question 73: An ammeter is used to detect the flow of electric current. The correct option is B. Question 74: The angle between the magnetic and geographical meridians is the angle of declination. The correct option is A. Question 75: The second medium must be rarer. The correct option is A.
Examples
Understanding these physics concepts is crucial in many real-world applications. For example, calculating electric power helps in designing efficient electrical appliances. Knowing about vector quantities is essential in mechanics for analyzing forces and motion. Understanding sound intensity is important in acoustics for designing sound systems and noise control. The principles of optics are used in designing lenses and optical instruments. These concepts form the foundation for many engineering and scientific fields.
