How can you know that anode or cathode rays are travelling in straight

1.	How can you know that anode or cathode rays are travelling in straight Line ?
Answer» William Crookes in 1879 demonstrated that cathode rays travel in straight lines. He placed an opaque object like metal cross in the path of cathode rays in a discharge tube. It was observed that a sharp shadow of the cross was cast on the glass behind the cross. A shadow of metal cross under the circumstances can be formed only if cathode rays travel in straight lines and cannot bend round the corners of the metal cross.

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