Two converging lenses, the first with focal length 25 cm and the second with focal length 20 cm, are separated by 30 cm. A 4.0 cm tall object is placed 50 cm in front of the first lens. Where is the final image?
A. 20 cm after the second lens
B. 20 cm before the second lens
C. 10 cm after the second lens
D. 10 cm before the second lens
E. 50 cm after the second lens
C. 10 cm after the second lens
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When viewed from above, suppose that a helicopter’s rotor spins clockwise. The helicopter engine must continually exert a torque on the rotor to keep it spinning against the drag that the air exerts on the rotor. Note that a helicopter is usually designed so its center of mass is directly under the rotor. In order for the helicopter to hover motionless in the air, a small rotor at the helicopter’s tail is necessary. As viewed by someone looking at the tail from the helicopter’s front, the small rotor must blow air
A. To the left. B. To the right. C. Vertically upward. D. Vertically downward. E. In some combination of these directions.
A long solenoid (1000 turns/m) carries a current of 25 mA and has an inside radius of 2.0 cm. A long wire which is parallel to and 4.0 cm from the axis of the solenoid carries a current of 6.0 A. What is the magnitude of the magnetic field at a point on the axis of the solenoid?
A. 51 ?T B. 61 ?T C. 43 ?T D. 81 ?T E. 1.4 ?T
The motion of atoms and molecules that most affects temperature is
A) translational. B) rotational. C) vibrational. D) none of the above
Suppose a fish is observed below the surface of a lake. The distance the fish appears below the surface when looking down from above into the water (n = 1.33) is
A. less than the fish's actual distance. B. equal to the fish's actual distance. C. greater than the fish's actual distance.