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An object moves from the position +34m to the position -15m in 15 seconds. what is it's total displacement? what is it's average velocity?

The horizontal blue line through the middle of the lens is called the optical axis. as the lamp is moved above or below the axis, keeping the horizontal distance to the center of the lens constant, how does the horizontal distance from the lens to the image change?

Consider an air-filled charged capacitor. how can its capacitance be increased?