Is a semibrive worth 1 beat?

Yes, a semibreve (or whole note) is worth 1 beat in some time signatures, particularly in 4/4 time where it can be held for the entire measure. However, in other time signatures, its duration may be interpreted differently, so it's essential to consider the context of the music. In general, the semibreve represents a longer duration compared to other notes, such as crotchets (quarter notes) or quavers (eighth notes).