describe how a reliable value of the focal length of a converging lens can be obtained by experiment​

The image shows a pendulum in simple harmonic motion the pendulum starts at a and swing to e

Which one of the following research methods can show cause and effect

When is a current produced? when the terminals of an electrochemical cell are connected by a wire if the electric circuit is opened in an electrochemical cell if the electrolyte is removed from an electrochemical cell when the electrodes are reversed in an electrochemical cell