64. An atom has 11 protons and 12 neutrons. Then the number of electrons in this atom is
A. 12
B. 11
C. 23
D. 1
65. 100 J of mechanical energy is supplied to 1 kg water which raises its temperature through
A. 100 K
B. 4200 K
C. [tex]$\left(\frac{1}{4200}\right)^{ K }$[/tex]
D. [tex]$\left(\frac{1}{42}\right)^{ K }$[/tex]
66. A person suffering from myopia has to use
A. biconvex lens
B. planoconvex lens
C. biconcave lens
D. concavoconvex lens
67. An object is placed at a distance of 20 cm from a convex lens of focal length 10 cm. The image formed by the lens will be
A. at 20 cm from the lens, inverted and real
B. at 20 cm from the lens, inverted and virtual
C. at 20 cm from the lens, erect and real
D. at 20 cm from the lens, erect and virtual
68. To find the direction of induced current in an electromagnetic induction,
A. Maxwell's cork screw rule is used
B. Right hand thumb rule is used
C. Fleming's right hand rule is used
D. Fleming's left hand rule is used
Answer (2)
The answers to the questions are: 64 - B, 65 - D, 66 - C, 67 - A, 68 - C. The reasoning involves understanding atomic structure, temperature changes using heat formulas, myopia correction methods, properties of lenses, and electromagnetic principles. Each answer is based on fundamental concepts in physics.
;
The number of electrons in a neutral atom equals the number of protons, so the answer to question 64 is B.
Use the formula Q = m c Δ T to find the temperature change, so the answer to question 65 is D.
Myopia is corrected using a biconcave lens, so the answer to question 66 is C.
Use the lens formula to find the image distance and characteristics, so the answer to question 67 is A.
Fleming's right-hand rule is used to determine the direction of induced current, so the answer to question 68 is C.
Final Answers: B, D, C, A, C. B , D , C , A , C
Explanation
Introduction Let's tackle these multiple-choice questions one by one, making sure we understand the reasoning behind each answer.
Question 64 - Electrons in an Atom Question 64: In a neutral atom, the number of electrons is equal to the number of protons. Since the atom has 11 protons, it must also have 11 electrons. Therefore, the answer is B.
Question 65 - Temperature Change of Water Question 65: We can use the formula Q = m c \[ De lt a ] T , where Q is the heat energy supplied, m is the mass of the water, c is the specific heat capacity of water, and \[ De lt a ] T is the change in temperature. We are given Q = 100 J , m = 1 kg , and c = 4200 J/kg K . We want to find \[ De lt a ] T . Rearranging the formula, we get: Delta]T = \frac{Q}{mc} = \frac{100}{1 \times 4200} = \frac{100}{4200} = \frac{1}{42} \text{ Therefore, the answer is D.
Question 66 - Correcting Myopia Question 66: Myopia, or nearsightedness, is corrected using a biconcave lens. This type of lens diverges light rays before they enter the eye, allowing the image to focus correctly on the retina. Therefore, the answer is C.
Question 67 - Image Formation by a Convex Lens Question 67: We can use the lens formula f 1 = v 1 + u 1 , where f is the focal length, v is the image distance, and u is the object distance. We are given f = 10 cm and u = − 20 cm (since the object is on the left side of the lens). We want to find v .
10 1 = v 1 + − 20 1 v 1 = 10 1 + 20 1 = 20 2 + 20 1 = 20 3 v = 3 20 ≈ 6.67 cm Since v is positive, the image is real. For a convex lens, when the object is placed beyond the focal length, the image is inverted. However, the calculation above is incorrect. Let's correct it: 10 1 = v 1 + − 20 1 v 1 = 10 1 − − 20 1 = 10 1 + 20 1 = 20 2 + 20 1 = 20 3 v = 3 20 cm Since u = − 20 cm = − 2 f , the image will be formed at 2 f on the other side, which is 20 cm . The image is real and inverted. Therefore, the answer is A.
Question 68 - Direction of Induced Current Question 68: Fleming's right-hand rule is used to find the direction of induced current in electromagnetic induction. Therefore, the answer is C.
Final Answers In summary:
Question 64: B
Question 65: D
Question 66: C
Question 67: A
Question 68: C
Examples
These physics concepts are fundamental to understanding how the world around us works. For example, understanding lenses helps us design cameras and telescopes. Knowing about heat transfer helps us build efficient engines and cooling systems. The principles of electromagnetism are used in generators and motors, which power much of our modern technology.
